DOI: 10.1002/chem.201403605
Communication
& Vinyl Carbenoids
Carbolithiation of Chloro-Substituted Alkynes: A New Access to Vinyl Carbenoids Rudy Lhermet,[a] Maha Ahmad,[a] Catherine Fressign,[a] Bernard Silvi,[b] Muriel Durandetti,*[a] and Jacques Maddaluno*[a] Abstract: The intramolecular carbolithiation of a series of chloro-substituted alkynes leads to exocyclic alkylidene carbenoids of which both nucleophilic and electrophilic characters can be drove. A sole stereoselective 5-exo-dig addition takes place, probably because of a strong and persisting Li–Cl interaction arising before the transition state.
Carbenoids are versatile reagents that juxtapose a metal and an electronegative element (generally an halogen) on the same carbon atom.[1] Because they cumulate a nucleophilic and an electrophilic character, these have found many applications for the C C bond formation in various fields of organic chemistry, from natural product synthesis,[2] heterocyclic chemistry,[3] C H activation[4] to cyclopropanation,[1a, 5d, 6c] or diverse homologation reactions.[6a–b] The metals implied in this chemistry go from lithium,[1b,c, 5] to magnesium,[7] zinc,[6] iron,[8] rhodium,[9] gold,[10] chromium.[11] The sp3 lithium-based carbenoids, first studied by Kçbrich in the 1960s,[12] are configurationally stable at low temperature and have found elegant applications in stereoselective synthesis.[13] The lithium sp2 analogues received attention later on, and it was shown that they exhibit a similar chameleon-like behavior, at the exception of the very limited cyclopropanation pathway. In his review, Braun underlines that three routes to vinylidene carbenoids have been identified, which are deprotonation, halogen–lithium exchange or transmetallation.[1b] We describe here a new access to this family of reagents based on an intramolecular carbolithiation reaction, giving precursors of five-membered heterocycles of fine synthetic value.[14] The carbometallation of simple internal alkynes affords trisubstituted vinylmetals, which can in turn trap an electrophile and yield tetrasubstituted olefins.[15] Generating vinylidene carbenoids by such a transformation requires that the electroneg[a] Dr. R. Lhermet, M. Ahmad, Dr. C. Fressign, Dr. M. Durandetti, Dr. J. Maddaluno Laboratoire COBRA, CNRS UMR 6014 & FR 3038, Univ. Rouen INSA Rouen, 76821 Mt St Aignan Cedex (France) E-mail: [email protected] [email protected] [b] Dr. B. Silvi Laboratoire de Chimie Thorique, CNRS UMR 7616 & FR 2622, UPMC 4 Place Jussieu, 75252 Paris Cedex (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201403605. Chem. Eur. J. 2014, 20, 10249 – 10254
ative element juxtaposed to the lithium is borne directly by the C C triple bond.[14c] Such a case is met seldom[15j] since the starting substrate has to combine a highly reactive nucleophilic center and a fragile and little activated electrophile, incompatible a priori. The stereocontrol of the newly created double bond is another standing problem. In general, the carbolithiations of alkynes are known to occur in a syn fashion.[16] Our own studies revealed that, at least in one case, the lithium cation can be steered by a proximal coordination.[17] We focused this study on chloroalkynes, precursors of canonical 1-halo-1-alkenyllithiums (Table 1). Chlorine was the halogen of choice since chloroalkynes are easily synthetized, while fluoroalkynes are known to be unstable and even explosive compounds.[18] On the other hand, bromoalkynes (and iodoalkynes) are more sensitive to halogen– lithium exchanges. Substrates 1 were prepared by chlorination of the corresponding lithium acetylides[19] by TsCl,[20a] CCl4[20b] or NCS.[19b] Treating 1 with nBuli (method A) or PhLi (method B) triggered the expected I–Li exchange, and the resulting aryllithium underwent rapid carbolithiation to afford the 5-exo-dig products 2 with total regio-, stereo- and chemoselectivity (Table 1). While nBuLi triggers some chlorine–lithium exchange (5–25 %, Table 1), PhLi affords, in all cases, a total conversion. The scope of this method is relatively large since propargylic ethers and “amides”, electron-withdrawing or donating substituents on the aromatic as well as a pyridine nucleus are tolerated. In all examples considered, the NOESY suggested that 2 are exclusively E (confirmed for 2 c by X-rays analysis) and result from the anti addition of the aryllithium on the triple bond. Note that if the conversions are generally good (see spectra in the Supporting Information), the isolated yields can be disappointing because of the exo- to endo-cyclic isomerization of the double bond during purification on silica gel, leading in most cases to an aromatic heterocycle.[21] The success of this carbolithiation is obviously related to the cyclic character of the gem-vinyllithium products 2-Li that are protected against the Fritsch–Buttenberg–Wiechell rearrangement.[22] This adverse reaction was the only one observed by Satoh et al. on an acyclic analogue.[23] Overall, the efficiency of the transformation of 1 persuaded us to further investigate the chemistry of these species. The juxtaposed electrophilic and nucleophilic characters of these reagents open opportunities in heterocyclic chemistry, as illustrated below for 2 a. The dual nature of 2 a-Li was first exemplified with (E)-pentenylchlorozirconocene, itself prepared by hydrozirconation of
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Communication Subsequently, we decided to evaluate the electrophilic character of 2 a and 12 taking advantage of the chlorovinyl appendage in Suzuki couplings with arylboronic acids (Table 3). Treating 2 a with 4-fluoroEntry Substrate Method Product Yield [%][a] phenyl boronic acid using a protocol inspired from Shen and 1 1a A 2a 90 (83) Fu[26] led stereospecifically to the expected trisubstituted olefin 13 in fine yield. Note that the styr2 1a B 2a 99 (92) enic product is not prone anymore to isomerization, the double bond remaining in its original exocyclic location. Pleas3 1b A 2b 72 (35) ingly enough, the chlorine in 12 reacts in similar conditions, affording the styrenic products 4 1b B 2b 95 (54) 14–16 (entries 2–4). The tributyltin appendage, untouched by this catalytic system, remains 5 1c B 2c 95 (55) available for a Stille coupling. Thus, 16 reacted with 2-iodoanisole in the presence of Pd2dba3 led in modest yield, but stereo1d B 2d 90 (59) 6 selectively, to the tetrasubstituted exocyclic olefin 17 (Scheme 2). 7 1e B 2e 99[b] (48) The reverse sequence (nucleophilic then electrophilic reactions) can similarly be set to work. Thus, the boronic acid 11 8 1f A 2f 75 (54) was coupled with PhI or 3-bromopyridine to provide the ex[a] Crude yield (isolated yield between parentheses). [b] See ref. [21]. pected tetrasubstituted chloroolefins 18 and 19 (Scheme 3). Conversions are good (see the crude mixture spectra in the Supporting Information) but the pent-1-yne by the Schwartz reagent.[24] The diene 3 was recovproducts are fragile on silica gel. Finally, the remaining chlorine ered stereoselectively in 62 % isolated yields (Scheme 1). The atom on 19 allowed the stereoselective introduction of mechanism is likely to include a nucleophilic Li Zr transmetalaa methyl by a Kumada coupling,[27] leading to 20. tion step then an electrophilic rearrangement of the intermediTo better understand the details of this reaction, we underate zirconate. took a DFT theoretical analysis of its mechanism.[28] In particuAdvantage could also be taken from the strong nucleophilic character of 2 a-Li, reacting this intermediate at low temperalar, we wished to probe the origin of the antiselectivity of the ture with classical electrophiles (Table 2).[25] The expected prod5-exo-dig process leading to 2 a-Li. The B3P86 functional and 6-31G** basis set were selected, in line with our previous reucts were obtained in average to good yields and full E stereosults.[17b,c] The zero point energy (ZPE) corrections were includselectivity. ed in these computations. The working model consisted in a monomeric lithioaryl 1 a-Li derived from 1,[29] solvated by two explicit molecules of THF.[30] The full optimization of 1 aLi·2 THF led to a “folded” conformer in which the triple bond faces the lithium cation.[17c] The transition state (TS) was then localized through a potential energy scan (PES) undertaken by decreasing the distance between the two connecting carbons. A reoptimization of this primary TS led to the “true” TS, which was properly characterized. Scheme 1. Insertion of vinylcarbenoid 2 a-Li into an organozirconocene. Table 1. Synthesis of vinyl carbenoids 2-Li from chloroalkynes 1.
Chem. Eur. J. 2014, 20, 10249 – 10254
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Communication tion is at the origin of the anticharacter of the carbolithiation Entry Electrophile Product Yield [%] depicted in Table 1. This halogen–lithium interaction is poorly documented, probably because 1 CD3CD2OD 4 77 (H/D = 1:9) the easy Cl–Li exchange process generally follows. In contrast, the F Li “bonding”, which does not 2 benzaldehyde 5 70 trigger an exchange, has been well characterized,[31] but, as mentioned above, the unsafe 3 crotonaldehyde (E/Z = 95:5) 6 59 (E/Z = 95:5) fluoroalkyne analogue of 1 a was not tested. Our calculations on 1-Li show that, beyond the TS, 4 acetone 7 70 the system progresses toward (E)-2 a-Li in an exothermic fashion ( 69.1 kcal mol 1, Figure 1). [a] 8 65 5 acetone Note the peculiar geometry of carbenoid 2 a-Li, the cation of which tends to align with the 6 benzylchloride 9 54 C=C double bond (C1C2Li = 167.48 while C1C2Cl = 113.58). This phenomenon, noted in 7 chlorotriisopropyl-silane 10 79 a previous DFT study on the bromine–lithium exchange in gemdibromo olefins,[32] can be as8 triisopropylborate 11 72 signed to the twofold interaction of Li + with the lone pairs of the vinyl on one hand and of the 12 70 9 tributylchloro-stannane chlorine on the other. An electron localization function (ELF) [a] Dehydration of 7 into 8 occurs at room temperature in a few hours. This result was obtained by leaving the analysis run on 2 a-Li supports crude reaction mixture for 3 days at room temperature before chromatography. this hypothesis. ELF relies on a topological approach of the chemical bond, which implicitly takes into account the superposition of the resonance forms and gives information on the electron reorganization induced by the rearrangement of the intermediates.[33] It also provides valuable pictures of the bonding in the hypervalent molecules. Figure 2 shows the lithium at the center of the tetrahedron formed by the chlorine, vinyl and two THF oxygen lone Scheme 2. Stille couplings on 16: access to tetrasubstituted olefins. Condition B: 5 % Pd2dba3, 10 % BINAP, 20 % CuI, 2 equiv CsF, toluene, 110 8C. pairs.[34] The results of a similar DFT study on the fluoro-, Table 2. Trapping of vinyl carbenoid 2 a-Li by various electrophiles.
Scheme 3. Suzuki/Kumada couplings on 11. Condition A: see the footnote in Table 3. Condition C: 10 % Pd(OAc)2, 20 % PCy3, THF, 50 8C.
The 5-exo-dig cyclization is associated to a low-lying TS (+7.8 kcal mol 1, Figure 1) at which a relatively short Li Cl distance is computed (2.76 ). Correlatively, the triple bond adopts a pro-E geometry. It thus seems that the Cl–Li interacChem. Eur. J. 2014, 20, 10249 – 10254
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Figure 1. Energy profile along the carbolithiation of 1 a-Li.
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Communication Experimental Section
Table 3. Suzuki coupling on 2 a and 12.
Typical carbolithiation procedure, exemplified with 2 a PhLi (1.8 m in Bu2O, 0.6 mL, 1.1 mmol) was added to a solution of iodoaryle 1 a (293 mg, 1 mmol) Entry E Ar-B(OH)2 Product Yield [%] in anhydrous THF (5 mL) under argon atmosphere at 78 8C. The mixture was stirred for 15 min at 1 H (2 a) 13 69 78 8C, then hydrolyzed with EtOH (2 mL) and diluted with water (5 mL). The aqueous layer was extracted with Et2O (2 10 mL) and the combined organic layers were 14 51 2 SnBu3 (12) washed with brine (10 mL), dried over anhydrous MgSO4 and then concentrated to afford the crude. The pure 2 a (154 mg, 0.92 mmol, 3 SnBu3 (12) 15 66 92 %) was isolated by flash chromatography on silica (1 % of Et2O in n-pentane) as a pale yellow oil. 1 H NMR (300 MHz, CDCl3)): d = 5.05 (d, J = 2.6 Hz, 2 H), 5.98 (t, J = 2.6 Hz, 1 H), 6.85 (dd, J = 8.2, 4 SnBu3 (12) 16 84 1.1 Hz, 1 H), 6.93 (td, J = 7.6, 1.1 Hz, 1 H), 7.26 (ddd, J = 8.2, 7.6, 1.2 Hz, 1 H), 8.03 ppm (dd, J = 7.6, 1.2 Hz, [a] Condition A: 10 % Pd(OAc)2, 20 % PCy3, 2 equiv K2CO3, THF/H2O (3:1), 50 8C. 1 H); 13C NMR (75 MHz, CDCl3): d = 74.3, 106.1, 110.4, 120.9, 124.1, 125.9, 131.3, 136.9, 164.6 ppm; bromo-, and iodoalkyne analogues of 1 a-Li, showing that not NMR 2D NOESY: correlation between 5.05 and 5.98; MS (EI, 70 eV) m/z: 167–169 [M + , base], 131 [M Cl]; HRMS (EI): calcd for [M + ] all halogens behave the same, will be detailed in a forthcoming C 9H7ClO: 166.0185, 168.0156; found: 166.0183, 168.0158. study.
Typical consecutive carbolithiation procedure, exemplified with 5
Figure 2. ELF representations of 2 a-Li. Color codes: cores (magenta), monosynaptic (orange) and disynaptic (green) valence basins. Hydrogen atoms are featured in light blue. Bounding isosurface: ELF = 0.85.
In conclusion, the intramolecular carbolithiation of chloroalkynes 1 is a chemo-, regio- and stereoselective reaction. Following a 5-exo-dig route, it affords anti carbolithiation products, probably because of a strong and persisting Li–Cl interaction arising before the transition state. The dual character of carbenoid 2-Li was illustrated by a set of reactions with varied electrophiles and nucleophiles. Overall, the carbolithiation of chloroalkynes can be regarded as a new way of generating vinyl carbenoids. Extension of this reaction to other heterosubstituted alkynes is underway.
nBuLi (1.6 m in hexanes, 344 mL, 0.55 mmol) was added to a solution of iodoaryle 1 a (146 mg, 0.5 mmol) in anhydrous THF (5 mL) under argon atmosphere at 78 8C. The mixture was stirred for 15 min before the addition of benzaldehyde (101 mL, 1 mmol), then 30 min at 78 8C and warmed to room temperature. The reaction was hydrolyzed after 30 min with water (5 mL) and the aqueous layer was extracted with Et2O (2 10 mL). The combined organic layers were washed with brine (10 mL), dried over anhydrous MgSO4, then concentrated. Recrystallization in n-pentane provided pure 5 (95 mg, 0.35 mmol, 70 %) as a white solid. 1H NMR (300 MHz, CDCl3): d = 2.57 (d, J = 6.6 Hz, 1 H), 5.24 (d, J = 14.7 Hz, 1 H), 5.35 (d, J = 14.7 Hz, 1 H), 5.45 (d, J = 6.6 Hz, 1 H), 6.89 (dd, J = 8.2, 1.3 Hz, 1 H), 6.96 (td, J = 7.7, 1.3 Hz, 1 H), 7.24–7.49 (m, 6 H), 8.13 ppm (dd, J = 7.7, 1.1 Hz, 1 H); 13C NMR (75 MHz, CDCl3): d = 74.0, 74.9, 110.4, 121.0, 122.6, 124.1, 126.0, 126.2 (2C), 128.5, 128.8 (2C), 131.4, 133.7, 139.7, 164.6 ppm; MS (EI, 70 eV) m/z: 272–274 [M + ], 254–256 [M H2O], 237 [M Cl], 219 [M Cl H2O, base]; m.p.: 99–101 8C; elemental analysis calcd (%) for C16H13ClO2 (272.73): C 70.46, H 4.80; found: C 70.84, H 4.85.
Acknowledgements R.L. and M.A. are grateful to the Rgion de Haute-Normandie, CNRS and CRUNCh interregional program for Ph.D. fellowships.
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Communication We acknowledge the Labex SynOrg (ANR-11-LABX-0029) for financial support of our general research projects. Computations were run at CRIHAN (St. Etienne-du-Rouvray). We warmly thank Prof. D. Harrowven (University of Southampton, UK) for helpful discussions. Keywords: carbolithiation · chloroalkyne · heterocycles · lithium · vinyl carbenoids [16] [1] a) M. Baumann, G. Kçbrich, Tetrahedron Lett. 1974, 15, 1217 – 1220; b) M. Braun, Angew. Chem. 1998, 110, 444 – 465; Angew. Chem. Int. Ed. 1998, 37, 430 – 451; c) G. Boche, J. C. W. Lohrenz, Chem. Rev. 2001, 101, 697 – 756; d) M. Braun, in Chemistry of Organolithium Compounds (Eds.: Z. Rappoport, I. Marek), Wiley, Chichester, 2006, Chap. 13, pp. 829 – 900; e) V. Capriati, S. Florio, Chem. Eur. J. 2010, 16, 4152 – 4162. [2] a) J. M. Meja-Oneto, A. Padwa, Org. Lett. 2006, 8, 3275 – 3278; b) H. M. L. Davies, J. R. Denton, Chem. Soc. Rev. 2009, 38, 3061 – 3071. [3] A. Padwa, S. K. Bur, Tetrahedron 2007, 63, 5341 – 5378. [4] a) R. H. Fisher, M. Baumann, G. Kçbrich, Tetrahedron Lett. 1974, 15, 1207 – 1208; b) H. M. L. Davies, J. R. Manning, Nature 2008, 451, 417 – 424. [5] a) T. Clark, P. v. R. Schleyer, Tetrahedron Lett. 1979, 20, 4963 – 4966; b) T. Clark, P. v. R. Schleyer, J. Am. Chem. Soc. 1979, 101, 7747 – 7748; c) K.-i. Sato, K. Suzuli, M. Ueda, M. Katayama, Y. Kajihara, Chem. Lett. 1991, 1469 – 1472; d) Z. Ke, Y. Zhou, H. Gao, C. Zhao, D. L. Phillips, Chem. Eur. J. 2007, 13, 6724 – 6731. [6] a) R. Hilgenkamp, C. K. Zercher, Org. Lett. 2001, 3, 3037 – 3040; b) Q. Pu, E. Wilson, C. K. Zercher, Tetrahedron 2008, 64, 8045 – 8051; c) J.-F. Fournier, S. Mathieu, A. B. Charette, J. Am. Chem. Soc. 2005, 127, 13140 – 13141. [7] a) G. Boche, K. Harms, M. Marsch, A. Mller, J. Chem. Soc. Chem. Commun. 1994, 1393 – 1394; b) T. Satoh, K. Takano, H. Ota, H. Someya, K. Matsuda, M. Koyama, Tetrahedron 1998, 54, 5557 – 5574; c) V. A. Vu, I. Marek, P. Knochel, Synthesis 2003, 12, 1797 – 1802; d) T. Satoh, Chem. Soc. Rev. 2007, 36, 1561 – 1572; e) N. Mori, K. Obuchi, T. Katae, J. Sakurada, T. Satoh, Tetrahedron 2009, 65, 3509 – 3517; f) R. H. V. Nishimura, F. T. Toledo, J. L. C. Lopes, G. C. Clososki, Tetrahedron Lett. 2013, 54, 287 – 290; g) G. Kashiwamura, T. Kimura, T. Satoh, Tetrahedron Lett. 2013, 54, 2533 – 2535. [8] a) M. Durandetti, J. Prichon, Synthesis 2006, 1542 – 1548; b) X.-L. Sun, J.-C. Zheng, Y. Tang, Pure Appl. Chem. 2010, 82, 625 – 634. [9] a) M. P. Doyle, R. J. Pieters, J. Taunton, H. Q. Pho, J. Org. Chem. 1991, 56, 820 – 829; b) A. Padwa, A. T. Price, J. Org. Chem. 1995, 60, 6258 – 6259; c) A. Padwa, M. A. Brodney, J. P. J. Marino, M. H. Osterhout, A. T. Price, J. Org. Chem. 1997, 62, 67 – 77. [10] a) G. Seidel, R. Mynott, A. Frstner, Angew. Chem. 2009, 121, 2548 – 2551; Angew. Chem. Int. Ed. 2009, 48, 2510 – 2513; b) Y. Zhou, B. G. Trewyn, R. J. Angelici, L. K. Woo, J. Am. Chem. Soc. 2009, 131, 11734 – 11743; c) F. Miege, C. Meyer, J. Cossy, Beilstein J. Org. Chem. 2011, 7, 717 – 734. [11] D. K. Barma, R. Baati, A. Valleix, C. Mioskowski, J. R. Falck, Org. Lett. 2001, 3, 4237 – 4238. [12] G. Kçbrich, Angew. Chem. 1967, 79, 15 – 27; Angew. Chem. Int. Ed. Engl. 1967, 6, 41 – 52. [13] See for instance: B. A. Pearlman, S. R. Putt, J. A. Fleming, J. Org. Chem. 2006, 71, 5646 – 5657. [14] See for instance: a) W. F.; Bailey, N. M. Wachter-Jurcsak, M. R. Pineau, T. V. Ovaska, R. R. Warren, C. E. Lewis, J. Org. Chem. 1996, 61, 8216 – 8228 Bailey, T. V. Ovaska, Tetrahedron Lett. 1990, 31, 627 – 630; b) J. M. Nuss, M. M. Murphy, R. A. Rennels, M. H. Heravi, R. J. Mohr, Tetrahedron Lett. 1993, 34, 3079 – 3082; c) R. L. Funk, G. L. Bolton, K. M. Brummond, K. E. Ellestad, J. B. Stallman, J. Am. Chem. Soc. 1993, 115, 7023 – 7024; d) Y. Liu, B. Shen, M. Kotora, T. Takahashi, Angew. Chem. 1999, 111, 966 – 968; Angew. Chem. Int. Ed. 1999, 38, 949 – 952; e) D. Bouyssi, G. Balme, Synlett 2001, 1191 – 1193; f) G. Zhu, Z. Zhang, Org. Lett. 2003, 5, 3645 – 3648; g) R. N. Richey, H. Yu, Org. Process Res. Dev. 2009, 13, 315 – 320. [15] Inter alia: a) I. Marek, N. Chinkov, D. Banon-Tenne, in Metal-Catalyzed Cross-Coupling Reactions (Eds.: F. Diederich, A. de Meijere), Wiley-VCH, Chem. Eur. J. 2014, 20, 10249 – 10254
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Weinheim, 2004, Chapt. 7, pp. 395 – 478; b) F. J. FaÇans, R. Sanz, in The chemistry of organolithium compounds, Vol. 2 (Eds.: Z. Rappoport, I. Marek), Wiley, Chichester, 2006, Chap. 4, pp. 295 – 379; c) J.-F. Normant, A. Alexakis, Synthesis 1981, 841 – 870; d) A.-M. L. Hogan, D. F. O’Shea, Chem. Commun. 2008, 3839 – 3851; e) S. Ma, Handbook of Cyclization Reactions, Vol. 1, Wiley-VCH, Weinheim, 2010; f) X. Jia, D. A. Petrone, M. Lautens, Angew. Chem. 2012, 124, 10008 – 10010; Angew. Chem. Int. Ed. 2012, 51, 9870 – 9872; g) Y. Minko, M. Pasco, H. Chechik, I. Marek, Beilstein J. Org. Chem. 2013, 9, 526 – 532; h) G. Gralla, B. Wibbeling, D. Hoppe, Org. Lett. 2002, 4, 2193 – 2195; i) W. Gati, M. M. Rammah, M. B. Rammah, F. Couty, G. Evano, J. Am. Chem. Soc. 2012, 134, 9078 – 9081. a) W. F. Bailey, T. V. Ovaska, T. K. Leipert, Tetrahedron Lett. 1989, 30, 3901 – 3904; b) W. F. Bailey, T. V. Ovaska, J. Am. Chem. Soc. 1993, 115, 3080 – 3090; c) W. F.; Bailey, N. M. Wachter-Jurcsak, M. R. Pineau, T. V. Ovaska, R. R. Warren, C. E. Lewis, J. Org. Chem. 1996, 61, 8216 – 8228; d) Y. Minko, I. Marek, in Lithium Compounds in Organic Synthesis (Eds.: R. Luisi, V. Capriati), Wiley-VCH, Weinheim, 2014, Chap. 11, pp. 329 – 350. a) F. Le Strat, J. Maddaluno, Org. Lett. 2002, 4, 2791 – 2793; b) C. Fressign, A.-L. Girard, M. Durandetti, J. Maddaluno, Angew. Chem. 2008, 120, 905 – 907; Angew. Chem. Int. Ed. 2008, 47, 891 – 893; c) C. Fressign, A.-L. Girard, M. Durandetti, J. Maddaluno, Chem. Eur. J. 2008, 14, 5159 – 5167. S. Y. Delavarenne, H. G. Viehe, in Chemistry of Acetylenes, Vol. 4 (Eds.: H. G. Viehe), Marcel Dekker, New York, 1969, p. 865; b) H. G. Viehe, Angew. Chem. 1965, 77, 768 – 773; Angew. Chem. Int. Ed. Engl. 1965, 4, 746 – 752. The acetylide is obtained by deprotonation by nBuLi or TBAT of the acetylenic precursor. For the first method, see ref. [17]. For the second method, see: a) Y. Sasson, O. W. Webster, J. Chem. Soc. Chem. Commun. 1992, 1200 – 1201; b) N. Gulia, B. Pigulski, M. Charewicz, S. Szafert, Chem. Eur. J. 2014, 20, 2746 – 2749. a) G. Cahiez, O. Gager, J. Buendia, Angew. Chem. 2010, 122, 1300 – 1303; Angew. Chem. Int. Ed. 2010, 49, 1278 – 1281; b) M. A. P. Martins, D. J. Emmerich, C. M. P. Pereira, W. Cunico, M. Rossato, N. Zanatta, H. G. Bonacorso, Tetrahedron Lett. 2004, 45, 4935 – 4938. The most stable 2 a converts into 3-chloromethylbenzofuran in 90 % yield in 3 days at RT, whereas compound 2 e alters quickly into indole so that a mixture of indoline and indole is recovered in the crude. a) P. Fritsch, Justus Liebigs Ann. Chem. 1894, 279, 319 – 323; b) W. P. Buttenberg, Justus Liebigs Ann. Chem. 1894, 279, 324 – 337; c) H. Wiechell, Justus Liebigs Ann. Chem. 1894, 279, 337 – 344; d) E. Jahnke, R. R. Tykwinski, Chem. Commun. 2010, 46, 3235 – 3249. T. Satoh, Y. Hayashi, K. Yamakawa, Bull. Chem. Soc. Jpn. 1993, 66, 1866 – 1869. a) E. Negishi, K. Akiyoshi, B. O’Connor, K. Takagi, G. Wu, J. Am. Chem. Soc. 1989, 111, 3089 – 3091; b) A. Kasatkin, R. J. Whitby, J. Am. Chem. Soc. 1999, 121, 7039 – 7049. For a similar radical-polar crossover domino reaction, see: a) A. PrezLuna, C. Botuha, F. Ferreira, F. Chemla, Chem. Eur. J. 2008, 14, 8784 – 8788; b) F. Chemla, F. Dulong, F. Ferreira, A. Prez-Luna, Beilstein J. Org. Chem. 2013, 9, 236 – 245. a) W. Shen, Tetrahedron Lett. 1997, 38, 5575 – 5578; b) A. F. Littke, G. C. Fu, Angew. Chem. 1998, 110, 3586 – 3587; Angew. Chem. Int. Ed. 1998, 37, 3387 – 3388. Z. Tan, E.-i. Negishi, Angew. Chem. 2006, 118, 776 – 779; Angew. Chem. Int. Ed. 2006, 45, 762 – 765. For a fine DFT study of a carbolithiation process, see: V. H. Gessner, S. G. Koller, C. Strohmann, A.-M. Hogan, D. F. O’Shea, Chem. Eur. J. 2011, 17, 2996 – 3004. A monomeric structure in THF is a reasonable assumption in view of: a) H. J. Reich, W. S. Goldenberg, A. W. Sanders, K. L. Jantzi, C. C. Tzschucke, J. Am. Chem. Soc. 2003, 125, 3509 – 3521. A tetramer is more likely in the solid state: b) A. Boman, D. Johnels, Magn. Reson. Chem. 2000, 38, 853 – 860. Solvation and conformation are discussed in: a) C. Fressign, R. Lhermet, A.-L. Girard, M. Durandetti, J. Maddaluno, J. Org. Chem. 2013, 78, 9659 – 9669. For related works, see: b) K. Ando, K. Morokuma, Theor. Chem. Acc. 2011, 130, 323 – 331; c) H. H. Incea, B. Dedeoglua, S. Gula, V. Aviyentea, I. Coldham, Mol. Phys. 2012, 110, 353 – 359; d) A. C. Voukides, K. J. Cahill, R. P. Johnson, J. Org. Chem. 2013, 78, 11815 – 11823. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Communication [31] a) X-ray: D. Stalke, U. Klingebiel, G. M. Sheldrick, Chem. Ber. 1988, 121, 1457 – 1459; computations: b) N. J. R. van Eikema Hommes, P. v. R. Schleyer, Angew. Chem. 1992, 104, 768 – 771; Angew. Chem. Int. Ed. Eng. 1992, 31, 755 – 759. Recently, the Cl – Zn interaction has been depicted: G. R. Stanton, P.-O. Norrby, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc. 2012, 134, 17599 – 17604. [32] K. Ando, J. Org. Chem. 2006, 71, 1837 – 1850. [33] For seminal papers, see: a) A. Becke, K. Edgecombe, J. Chem. Phys. 1990, 92, 5397 – 5403; b) B. Silvi, A. Savin, Nature 1994, 371, 683 – 686; c) A. Savin, R. Nesper, S. Wengert, T. F. F ssler, Angew. Chem. 1997, 109, 1892 – 1918; Angew. Chem. Int. Ed. Eng. 1997, 36, 1808 – 1832; d) B. Silvi, I. Fourr, E. A. Alikhani, Monatsh. Chem. 2005, 136, 855 – 879. For applications to organometallic chemistry, see: e) D. B. Chesnut, J. Phys. Chem.
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A 2000, 104, 7635 – 7638; f) C. Fressign, J. Maddaluno, A. Marquez, C. Giessner-Prettre, J. Org. Chem. 2000, 65, 8899 – 8907; g) E. Matito, J. Poater, F. M. Bickelhaupt, M. Sola, J. Phys. Chem. B 2006, 110, 7189 – 7198. [34] Considering monomeric 2 a-Li in THF is in line with the data presented in a) R. Knorr, T. Menke, K. Ferchland, Organometallics 2013, 32, 468 – 472. However, the substituent on the vinylic position can affect the aggregation of such species: b) R. Knorr, J. Freudenreich, K. Polborn, H. Nçth, G. Linti, Tetrahedron 1994, 50, 5845 – 5860.
Received: May 20, 2014 Published online on July 17, 2014
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& Vinyl Carbenoids
Carbolithiation of Chloro-Substituted Alkynes: A New Access to Vinyl Carbenoids Rudy Lhermet,[a] Maha Ahmad,[a] Catherine Fressign,[a] Bernard Silvi,[b] Muriel Durandetti,*[a] and Jacques Maddaluno*[a] Abstract: The intramolecular carbolithiation of a series of chloro-substituted alkynes leads to exocyclic alkylidene carbenoids of which both nucleophilic and electrophilic characters can be drove. A sole stereoselective 5-exo-dig addition takes place, probably because of a strong and persisting Li–Cl interaction arising before the transition state.
Carbenoids are versatile reagents that juxtapose a metal and an electronegative element (generally an halogen) on the same carbon atom.[1] Because they cumulate a nucleophilic and an electrophilic character, these have found many applications for the C C bond formation in various fields of organic chemistry, from natural product synthesis,[2] heterocyclic chemistry,[3] C H activation[4] to cyclopropanation,[1a, 5d, 6c] or diverse homologation reactions.[6a–b] The metals implied in this chemistry go from lithium,[1b,c, 5] to magnesium,[7] zinc,[6] iron,[8] rhodium,[9] gold,[10] chromium.[11] The sp3 lithium-based carbenoids, first studied by Kçbrich in the 1960s,[12] are configurationally stable at low temperature and have found elegant applications in stereoselective synthesis.[13] The lithium sp2 analogues received attention later on, and it was shown that they exhibit a similar chameleon-like behavior, at the exception of the very limited cyclopropanation pathway. In his review, Braun underlines that three routes to vinylidene carbenoids have been identified, which are deprotonation, halogen–lithium exchange or transmetallation.[1b] We describe here a new access to this family of reagents based on an intramolecular carbolithiation reaction, giving precursors of five-membered heterocycles of fine synthetic value.[14] The carbometallation of simple internal alkynes affords trisubstituted vinylmetals, which can in turn trap an electrophile and yield tetrasubstituted olefins.[15] Generating vinylidene carbenoids by such a transformation requires that the electroneg[a] Dr. R. Lhermet, M. Ahmad, Dr. C. Fressign, Dr. M. Durandetti, Dr. J. Maddaluno Laboratoire COBRA, CNRS UMR 6014 & FR 3038, Univ. Rouen INSA Rouen, 76821 Mt St Aignan Cedex (France) E-mail: [email protected] [email protected] [b] Dr. B. Silvi Laboratoire de Chimie Thorique, CNRS UMR 7616 & FR 2622, UPMC 4 Place Jussieu, 75252 Paris Cedex (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201403605. Chem. Eur. J. 2014, 20, 10249 – 10254
ative element juxtaposed to the lithium is borne directly by the C C triple bond.[14c] Such a case is met seldom[15j] since the starting substrate has to combine a highly reactive nucleophilic center and a fragile and little activated electrophile, incompatible a priori. The stereocontrol of the newly created double bond is another standing problem. In general, the carbolithiations of alkynes are known to occur in a syn fashion.[16] Our own studies revealed that, at least in one case, the lithium cation can be steered by a proximal coordination.[17] We focused this study on chloroalkynes, precursors of canonical 1-halo-1-alkenyllithiums (Table 1). Chlorine was the halogen of choice since chloroalkynes are easily synthetized, while fluoroalkynes are known to be unstable and even explosive compounds.[18] On the other hand, bromoalkynes (and iodoalkynes) are more sensitive to halogen– lithium exchanges. Substrates 1 were prepared by chlorination of the corresponding lithium acetylides[19] by TsCl,[20a] CCl4[20b] or NCS.[19b] Treating 1 with nBuli (method A) or PhLi (method B) triggered the expected I–Li exchange, and the resulting aryllithium underwent rapid carbolithiation to afford the 5-exo-dig products 2 with total regio-, stereo- and chemoselectivity (Table 1). While nBuLi triggers some chlorine–lithium exchange (5–25 %, Table 1), PhLi affords, in all cases, a total conversion. The scope of this method is relatively large since propargylic ethers and “amides”, electron-withdrawing or donating substituents on the aromatic as well as a pyridine nucleus are tolerated. In all examples considered, the NOESY suggested that 2 are exclusively E (confirmed for 2 c by X-rays analysis) and result from the anti addition of the aryllithium on the triple bond. Note that if the conversions are generally good (see spectra in the Supporting Information), the isolated yields can be disappointing because of the exo- to endo-cyclic isomerization of the double bond during purification on silica gel, leading in most cases to an aromatic heterocycle.[21] The success of this carbolithiation is obviously related to the cyclic character of the gem-vinyllithium products 2-Li that are protected against the Fritsch–Buttenberg–Wiechell rearrangement.[22] This adverse reaction was the only one observed by Satoh et al. on an acyclic analogue.[23] Overall, the efficiency of the transformation of 1 persuaded us to further investigate the chemistry of these species. The juxtaposed electrophilic and nucleophilic characters of these reagents open opportunities in heterocyclic chemistry, as illustrated below for 2 a. The dual nature of 2 a-Li was first exemplified with (E)-pentenylchlorozirconocene, itself prepared by hydrozirconation of
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Communication Subsequently, we decided to evaluate the electrophilic character of 2 a and 12 taking advantage of the chlorovinyl appendage in Suzuki couplings with arylboronic acids (Table 3). Treating 2 a with 4-fluoroEntry Substrate Method Product Yield [%][a] phenyl boronic acid using a protocol inspired from Shen and 1 1a A 2a 90 (83) Fu[26] led stereospecifically to the expected trisubstituted olefin 13 in fine yield. Note that the styr2 1a B 2a 99 (92) enic product is not prone anymore to isomerization, the double bond remaining in its original exocyclic location. Pleas3 1b A 2b 72 (35) ingly enough, the chlorine in 12 reacts in similar conditions, affording the styrenic products 4 1b B 2b 95 (54) 14–16 (entries 2–4). The tributyltin appendage, untouched by this catalytic system, remains 5 1c B 2c 95 (55) available for a Stille coupling. Thus, 16 reacted with 2-iodoanisole in the presence of Pd2dba3 led in modest yield, but stereo1d B 2d 90 (59) 6 selectively, to the tetrasubstituted exocyclic olefin 17 (Scheme 2). 7 1e B 2e 99[b] (48) The reverse sequence (nucleophilic then electrophilic reactions) can similarly be set to work. Thus, the boronic acid 11 8 1f A 2f 75 (54) was coupled with PhI or 3-bromopyridine to provide the ex[a] Crude yield (isolated yield between parentheses). [b] See ref. [21]. pected tetrasubstituted chloroolefins 18 and 19 (Scheme 3). Conversions are good (see the crude mixture spectra in the Supporting Information) but the pent-1-yne by the Schwartz reagent.[24] The diene 3 was recovproducts are fragile on silica gel. Finally, the remaining chlorine ered stereoselectively in 62 % isolated yields (Scheme 1). The atom on 19 allowed the stereoselective introduction of mechanism is likely to include a nucleophilic Li Zr transmetalaa methyl by a Kumada coupling,[27] leading to 20. tion step then an electrophilic rearrangement of the intermediTo better understand the details of this reaction, we underate zirconate. took a DFT theoretical analysis of its mechanism.[28] In particuAdvantage could also be taken from the strong nucleophilic character of 2 a-Li, reacting this intermediate at low temperalar, we wished to probe the origin of the antiselectivity of the ture with classical electrophiles (Table 2).[25] The expected prod5-exo-dig process leading to 2 a-Li. The B3P86 functional and 6-31G** basis set were selected, in line with our previous reucts were obtained in average to good yields and full E stereosults.[17b,c] The zero point energy (ZPE) corrections were includselectivity. ed in these computations. The working model consisted in a monomeric lithioaryl 1 a-Li derived from 1,[29] solvated by two explicit molecules of THF.[30] The full optimization of 1 aLi·2 THF led to a “folded” conformer in which the triple bond faces the lithium cation.[17c] The transition state (TS) was then localized through a potential energy scan (PES) undertaken by decreasing the distance between the two connecting carbons. A reoptimization of this primary TS led to the “true” TS, which was properly characterized. Scheme 1. Insertion of vinylcarbenoid 2 a-Li into an organozirconocene. Table 1. Synthesis of vinyl carbenoids 2-Li from chloroalkynes 1.
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Communication tion is at the origin of the anticharacter of the carbolithiation Entry Electrophile Product Yield [%] depicted in Table 1. This halogen–lithium interaction is poorly documented, probably because 1 CD3CD2OD 4 77 (H/D = 1:9) the easy Cl–Li exchange process generally follows. In contrast, the F Li “bonding”, which does not 2 benzaldehyde 5 70 trigger an exchange, has been well characterized,[31] but, as mentioned above, the unsafe 3 crotonaldehyde (E/Z = 95:5) 6 59 (E/Z = 95:5) fluoroalkyne analogue of 1 a was not tested. Our calculations on 1-Li show that, beyond the TS, 4 acetone 7 70 the system progresses toward (E)-2 a-Li in an exothermic fashion ( 69.1 kcal mol 1, Figure 1). [a] 8 65 5 acetone Note the peculiar geometry of carbenoid 2 a-Li, the cation of which tends to align with the 6 benzylchloride 9 54 C=C double bond (C1C2Li = 167.48 while C1C2Cl = 113.58). This phenomenon, noted in 7 chlorotriisopropyl-silane 10 79 a previous DFT study on the bromine–lithium exchange in gemdibromo olefins,[32] can be as8 triisopropylborate 11 72 signed to the twofold interaction of Li + with the lone pairs of the vinyl on one hand and of the 12 70 9 tributylchloro-stannane chlorine on the other. An electron localization function (ELF) [a] Dehydration of 7 into 8 occurs at room temperature in a few hours. This result was obtained by leaving the analysis run on 2 a-Li supports crude reaction mixture for 3 days at room temperature before chromatography. this hypothesis. ELF relies on a topological approach of the chemical bond, which implicitly takes into account the superposition of the resonance forms and gives information on the electron reorganization induced by the rearrangement of the intermediates.[33] It also provides valuable pictures of the bonding in the hypervalent molecules. Figure 2 shows the lithium at the center of the tetrahedron formed by the chlorine, vinyl and two THF oxygen lone Scheme 2. Stille couplings on 16: access to tetrasubstituted olefins. Condition B: 5 % Pd2dba3, 10 % BINAP, 20 % CuI, 2 equiv CsF, toluene, 110 8C. pairs.[34] The results of a similar DFT study on the fluoro-, Table 2. Trapping of vinyl carbenoid 2 a-Li by various electrophiles.
Scheme 3. Suzuki/Kumada couplings on 11. Condition A: see the footnote in Table 3. Condition C: 10 % Pd(OAc)2, 20 % PCy3, THF, 50 8C.
The 5-exo-dig cyclization is associated to a low-lying TS (+7.8 kcal mol 1, Figure 1) at which a relatively short Li Cl distance is computed (2.76 ). Correlatively, the triple bond adopts a pro-E geometry. It thus seems that the Cl–Li interacChem. Eur. J. 2014, 20, 10249 – 10254
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Figure 1. Energy profile along the carbolithiation of 1 a-Li.
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Table 3. Suzuki coupling on 2 a and 12.
Typical carbolithiation procedure, exemplified with 2 a PhLi (1.8 m in Bu2O, 0.6 mL, 1.1 mmol) was added to a solution of iodoaryle 1 a (293 mg, 1 mmol) Entry E Ar-B(OH)2 Product Yield [%] in anhydrous THF (5 mL) under argon atmosphere at 78 8C. The mixture was stirred for 15 min at 1 H (2 a) 13 69 78 8C, then hydrolyzed with EtOH (2 mL) and diluted with water (5 mL). The aqueous layer was extracted with Et2O (2 10 mL) and the combined organic layers were 14 51 2 SnBu3 (12) washed with brine (10 mL), dried over anhydrous MgSO4 and then concentrated to afford the crude. The pure 2 a (154 mg, 0.92 mmol, 3 SnBu3 (12) 15 66 92 %) was isolated by flash chromatography on silica (1 % of Et2O in n-pentane) as a pale yellow oil. 1 H NMR (300 MHz, CDCl3)): d = 5.05 (d, J = 2.6 Hz, 2 H), 5.98 (t, J = 2.6 Hz, 1 H), 6.85 (dd, J = 8.2, 4 SnBu3 (12) 16 84 1.1 Hz, 1 H), 6.93 (td, J = 7.6, 1.1 Hz, 1 H), 7.26 (ddd, J = 8.2, 7.6, 1.2 Hz, 1 H), 8.03 ppm (dd, J = 7.6, 1.2 Hz, [a] Condition A: 10 % Pd(OAc)2, 20 % PCy3, 2 equiv K2CO3, THF/H2O (3:1), 50 8C. 1 H); 13C NMR (75 MHz, CDCl3): d = 74.3, 106.1, 110.4, 120.9, 124.1, 125.9, 131.3, 136.9, 164.6 ppm; bromo-, and iodoalkyne analogues of 1 a-Li, showing that not NMR 2D NOESY: correlation between 5.05 and 5.98; MS (EI, 70 eV) m/z: 167–169 [M + , base], 131 [M Cl]; HRMS (EI): calcd for [M + ] all halogens behave the same, will be detailed in a forthcoming C 9H7ClO: 166.0185, 168.0156; found: 166.0183, 168.0158. study.
Typical consecutive carbolithiation procedure, exemplified with 5
Figure 2. ELF representations of 2 a-Li. Color codes: cores (magenta), monosynaptic (orange) and disynaptic (green) valence basins. Hydrogen atoms are featured in light blue. Bounding isosurface: ELF = 0.85.
In conclusion, the intramolecular carbolithiation of chloroalkynes 1 is a chemo-, regio- and stereoselective reaction. Following a 5-exo-dig route, it affords anti carbolithiation products, probably because of a strong and persisting Li–Cl interaction arising before the transition state. The dual character of carbenoid 2-Li was illustrated by a set of reactions with varied electrophiles and nucleophiles. Overall, the carbolithiation of chloroalkynes can be regarded as a new way of generating vinyl carbenoids. Extension of this reaction to other heterosubstituted alkynes is underway.
nBuLi (1.6 m in hexanes, 344 mL, 0.55 mmol) was added to a solution of iodoaryle 1 a (146 mg, 0.5 mmol) in anhydrous THF (5 mL) under argon atmosphere at 78 8C. The mixture was stirred for 15 min before the addition of benzaldehyde (101 mL, 1 mmol), then 30 min at 78 8C and warmed to room temperature. The reaction was hydrolyzed after 30 min with water (5 mL) and the aqueous layer was extracted with Et2O (2 10 mL). The combined organic layers were washed with brine (10 mL), dried over anhydrous MgSO4, then concentrated. Recrystallization in n-pentane provided pure 5 (95 mg, 0.35 mmol, 70 %) as a white solid. 1H NMR (300 MHz, CDCl3): d = 2.57 (d, J = 6.6 Hz, 1 H), 5.24 (d, J = 14.7 Hz, 1 H), 5.35 (d, J = 14.7 Hz, 1 H), 5.45 (d, J = 6.6 Hz, 1 H), 6.89 (dd, J = 8.2, 1.3 Hz, 1 H), 6.96 (td, J = 7.7, 1.3 Hz, 1 H), 7.24–7.49 (m, 6 H), 8.13 ppm (dd, J = 7.7, 1.1 Hz, 1 H); 13C NMR (75 MHz, CDCl3): d = 74.0, 74.9, 110.4, 121.0, 122.6, 124.1, 126.0, 126.2 (2C), 128.5, 128.8 (2C), 131.4, 133.7, 139.7, 164.6 ppm; MS (EI, 70 eV) m/z: 272–274 [M + ], 254–256 [M H2O], 237 [M Cl], 219 [M Cl H2O, base]; m.p.: 99–101 8C; elemental analysis calcd (%) for C16H13ClO2 (272.73): C 70.46, H 4.80; found: C 70.84, H 4.85.
Acknowledgements R.L. and M.A. are grateful to the Rgion de Haute-Normandie, CNRS and CRUNCh interregional program for Ph.D. fellowships.
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Communication We acknowledge the Labex SynOrg (ANR-11-LABX-0029) for financial support of our general research projects. Computations were run at CRIHAN (St. Etienne-du-Rouvray). We warmly thank Prof. D. Harrowven (University of Southampton, UK) for helpful discussions. Keywords: carbolithiation · chloroalkyne · heterocycles · lithium · vinyl carbenoids [16] [1] a) M. Baumann, G. Kçbrich, Tetrahedron Lett. 1974, 15, 1217 – 1220; b) M. Braun, Angew. Chem. 1998, 110, 444 – 465; Angew. Chem. Int. Ed. 1998, 37, 430 – 451; c) G. Boche, J. C. W. Lohrenz, Chem. Rev. 2001, 101, 697 – 756; d) M. Braun, in Chemistry of Organolithium Compounds (Eds.: Z. Rappoport, I. Marek), Wiley, Chichester, 2006, Chap. 13, pp. 829 – 900; e) V. Capriati, S. Florio, Chem. Eur. J. 2010, 16, 4152 – 4162. [2] a) J. M. Meja-Oneto, A. Padwa, Org. Lett. 2006, 8, 3275 – 3278; b) H. M. L. Davies, J. R. Denton, Chem. Soc. Rev. 2009, 38, 3061 – 3071. [3] A. Padwa, S. K. Bur, Tetrahedron 2007, 63, 5341 – 5378. [4] a) R. H. Fisher, M. Baumann, G. Kçbrich, Tetrahedron Lett. 1974, 15, 1207 – 1208; b) H. M. L. Davies, J. R. Manning, Nature 2008, 451, 417 – 424. [5] a) T. Clark, P. v. R. Schleyer, Tetrahedron Lett. 1979, 20, 4963 – 4966; b) T. Clark, P. v. R. Schleyer, J. Am. Chem. Soc. 1979, 101, 7747 – 7748; c) K.-i. Sato, K. Suzuli, M. Ueda, M. Katayama, Y. Kajihara, Chem. Lett. 1991, 1469 – 1472; d) Z. Ke, Y. Zhou, H. Gao, C. Zhao, D. L. Phillips, Chem. Eur. J. 2007, 13, 6724 – 6731. [6] a) R. Hilgenkamp, C. K. Zercher, Org. Lett. 2001, 3, 3037 – 3040; b) Q. Pu, E. Wilson, C. K. Zercher, Tetrahedron 2008, 64, 8045 – 8051; c) J.-F. Fournier, S. Mathieu, A. B. Charette, J. Am. Chem. Soc. 2005, 127, 13140 – 13141. [7] a) G. Boche, K. Harms, M. Marsch, A. Mller, J. Chem. Soc. Chem. Commun. 1994, 1393 – 1394; b) T. Satoh, K. Takano, H. Ota, H. Someya, K. Matsuda, M. Koyama, Tetrahedron 1998, 54, 5557 – 5574; c) V. A. Vu, I. Marek, P. Knochel, Synthesis 2003, 12, 1797 – 1802; d) T. Satoh, Chem. Soc. Rev. 2007, 36, 1561 – 1572; e) N. Mori, K. Obuchi, T. Katae, J. Sakurada, T. Satoh, Tetrahedron 2009, 65, 3509 – 3517; f) R. H. V. Nishimura, F. T. Toledo, J. L. C. Lopes, G. C. Clososki, Tetrahedron Lett. 2013, 54, 287 – 290; g) G. Kashiwamura, T. Kimura, T. Satoh, Tetrahedron Lett. 2013, 54, 2533 – 2535. [8] a) M. Durandetti, J. Prichon, Synthesis 2006, 1542 – 1548; b) X.-L. Sun, J.-C. Zheng, Y. Tang, Pure Appl. Chem. 2010, 82, 625 – 634. [9] a) M. P. Doyle, R. J. Pieters, J. Taunton, H. Q. Pho, J. Org. Chem. 1991, 56, 820 – 829; b) A. Padwa, A. T. Price, J. Org. Chem. 1995, 60, 6258 – 6259; c) A. Padwa, M. A. Brodney, J. P. J. Marino, M. H. Osterhout, A. T. Price, J. Org. Chem. 1997, 62, 67 – 77. [10] a) G. Seidel, R. Mynott, A. Frstner, Angew. Chem. 2009, 121, 2548 – 2551; Angew. Chem. Int. Ed. 2009, 48, 2510 – 2513; b) Y. Zhou, B. G. Trewyn, R. J. Angelici, L. K. Woo, J. Am. Chem. Soc. 2009, 131, 11734 – 11743; c) F. Miege, C. Meyer, J. Cossy, Beilstein J. Org. Chem. 2011, 7, 717 – 734. [11] D. K. Barma, R. Baati, A. Valleix, C. Mioskowski, J. R. Falck, Org. Lett. 2001, 3, 4237 – 4238. [12] G. Kçbrich, Angew. Chem. 1967, 79, 15 – 27; Angew. Chem. Int. Ed. Engl. 1967, 6, 41 – 52. [13] See for instance: B. A. Pearlman, S. R. Putt, J. A. Fleming, J. Org. Chem. 2006, 71, 5646 – 5657. [14] See for instance: a) W. F.; Bailey, N. M. Wachter-Jurcsak, M. R. Pineau, T. V. Ovaska, R. R. Warren, C. E. Lewis, J. Org. Chem. 1996, 61, 8216 – 8228 Bailey, T. V. Ovaska, Tetrahedron Lett. 1990, 31, 627 – 630; b) J. M. Nuss, M. M. Murphy, R. A. Rennels, M. H. Heravi, R. J. Mohr, Tetrahedron Lett. 1993, 34, 3079 – 3082; c) R. L. Funk, G. L. Bolton, K. M. Brummond, K. E. Ellestad, J. B. Stallman, J. Am. Chem. Soc. 1993, 115, 7023 – 7024; d) Y. Liu, B. Shen, M. Kotora, T. Takahashi, Angew. Chem. 1999, 111, 966 – 968; Angew. Chem. Int. Ed. 1999, 38, 949 – 952; e) D. Bouyssi, G. Balme, Synlett 2001, 1191 – 1193; f) G. Zhu, Z. Zhang, Org. Lett. 2003, 5, 3645 – 3648; g) R. N. Richey, H. Yu, Org. Process Res. Dev. 2009, 13, 315 – 320. [15] Inter alia: a) I. Marek, N. Chinkov, D. Banon-Tenne, in Metal-Catalyzed Cross-Coupling Reactions (Eds.: F. Diederich, A. de Meijere), Wiley-VCH, Chem. Eur. J. 2014, 20, 10249 – 10254
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Received: May 20, 2014 Published online on July 17, 2014
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