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Asymmetric α-amination reaction of alkenyl trifluoroacetates catalyzed by a chiral phosphine–silver complex† Akira Yanagisawa,* Ryoji Miyake and Kazuhiro Yoshida
Received 23rd October 2013, Accepted 21st January 2014
The asymmetric α-amination of alkenyl trifluoroacetates with dialkyl azodicarboxylates catalyzed by the
DOI: 10.1039/c3ob42111b
DTBM-SEGPHOS·AgOTf complex takes place in the presence of 2,2,2-trifluoroethanol with almost
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quantitative yield and high ees of up to 97%.
Introduction The catalytic asymmetric α-amination reaction of carbonyl compounds is a beneficial way to form optically active α-amino carbonyl compounds, including α-amino acids and their derivatives; the functional groups are often seen in natural products or pharmaceutical compounds.1 Since the first report of the catalytic enantioselective α-amination of carbonyl compounds using azodicarboxylates as the electrophilic nitrogen source by Evans and Nelson in 1997,2 various methods that employ chiral catalysts have emerged, affording such α-aminated products in high yields and satisfactory optical purities.3,4 In the case of chiral metal complex catalyzed asymmetric transformations via chiral metal enolates, however, most of the protocols use readily enolizable carbonyl compounds as substrates,2,3b,c and as far as we know, there is no example of the catalytic reaction via a chiral metal enolate derived from simple ketones. We report here a novel example of the enantioselective α-amination reaction of simple-ketonederived alkenyl trifluoroacetates with dialkyl azodicarboxylates using the DTBM-SEGPHOS·AgOTf complex as the asymmetric catalyst in the presence of 2,2,2-trifluoroethanol (Scheme 1). The reaction is assumed to proceed via a chiral silver enolate.
Scheme 1 Chiral-silver-catalyzed asymmetric α-amination reaction of alkenyl trifluoroacetates with dialkyl azodicarboxylates.
Department of Chemistry, Graduate School of Science, Chiba University, Inage, Chiba 263-8522, Japan. E-mail: [email protected]; Fax: +81-(0)43-290-2789; Tel: +81-(0)43-290-2789 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ob42111b
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Results and discussion Kobayashi et al. reported that silver salts catalyzed the amination of silyl enol ethers with azo diester compounds.5 An asymmetric version of this reaction was achieved by the same group using BINAP as the chiral ligand.6 In contrast, we found that a chiral phosphine–silver(I) complex acted as the chiral cocatalyst in the asymmetric α-aminooxylation (O-nitroso aldol reaction) of alkenyl trichloroacetates with nitrosoarenes catalyzed by dibutyltin dimethoxide.7 The reaction took place through a tin enolate and the tin dimethoxide was regenerated in the presence of MeOH. In addition, the chiral phosphine– silver(I) complex was considered to activate a nitrosoarene through its coordination to the nitrogen atom. We envisioned that if azo diester compounds could be applied instead of nitrosoarenes to the dual catalyst system, the asymmetric α-amination of alkenyl esters would be possible. Thus, we investigated the suitability of an azo diester as an electrophile for the reaction. When a 1.2 : 1 mixture of alkenyl trifluoroacetate 1a8 and dimethyl azodicarboxylate (2a) was treated with (R)-DTBM-SEGPHOS (6 mol%), AgOTf (5 mol%), and Bu2Sn(OMe)2 (20 mol%) in the presence of MeOH (5 equiv.) and CF3CH2OH (10 equiv.) in THF at −40 °C for 2 h, targeted product 3aa was obtained quantitatively with 69% ee (Table 1, entry 1). Then, we studied the additive effect of a tertiary amine on the enantioselectivity and found that the enantiomeric excess of 3aa increased to 86% in the presence of 5 mol% of N,N-dimethylaniline (entry 2). The presence of Bu2Sn(OMe)2 is not necessary for the present catalytic system; for instance, the reaction proceeded smoothly in the absence of this catalyst at −40 °C to give the desired α-aminated product 3aa without significantly decreasing its ee (entry 3 vs. entry 2). Then, we screened for chiral phosphine ligands and found that DTBM-SEGPHOS was the ligand of choice (entries 3–7). As an additional optimization trial, we examined the solvent effect without PhNMe2 (entries 8–11) and found that the use of
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Table 1
Organic & Biomolecular Chemistry Optimization of the reaction conditions
Entry
Chiral phosphine
x
y
z
Solvent
T (°C)
Time (h)
Yielda (%)
eeb (%)
1c 2c,d 3d,e 4d 5d 6d 7d 8 9 10 11 12 13 14 15 16 17
(R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (S)-BINAP (R)-SEGPHOS (R)-DM-SEGPHOS (R,R)-t-Bu-QuinoxP* (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS
6 6 6 6 6 6 6 6 6 6 6 5 5 2 2 2 2
5 5 5 5 5 5 5 5 5 5 5 5 5 2 2 2 2
10 10 10 10 10 10 10 10 10 10 10 10 20 20 20 20 —
THF THF THF THF THF THF THF THF DMF THF–DMF (1 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF DMF CF3CH2OH
−40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −78 −78 −78 −78 −40
2 1 2 20 20 20 20 1 1 1 1 1 15 15 42 30 24
>99 >99 >99 60 70 52 14 >99 >99 >99 >99 >99 >99 >99 70 >99 40
69 86 85 41 11 60 14 81 76 90 91 92 95 95 93 82 99 >99 >99 99
71
Me i-Pr
15 11
3aa 3ac
>99 >99
95 97
2a
Me
16
3ca
>99
96
5 6
2a 2c
Me i-Pr
11 16
3da 3dc
>99 >99
90 96
7
2a
Me
15
3ca
>99
30
8
2b
Et
18
3fb
>99
17 (S)c
9
2a
Me
21
3ga
>99
31
Time (h)
Me
2a 2c
4
Azo diester
R
1
2a
2 3
Entry
a
Alkenyl ester
4
Isolated yield. b Determined by HPLC analysis. c The absolute configuration is shown in parentheses.
and 6). The reaction of acyclic alkenyl trifluoroacetate 1f (E/Z = 1/9) with azo diester 2b also furnished an α-aminated product in an almost quantitative yield under the standard reaction conditions, but the optical purity (17% ee) was low (entry 8). Substitution of the methyl group of 1f with n-propyl group raised the enantioselectivity (entry 9). A plausible catalytic cycle is shown in Fig. 1. First, (R)DTBM-SEGPHOS·AgOTf reacts with 2,2,2-trifluoroethanol10 in the presence of an appropriate amine, such as azo diester 2 or α-aminated product 3, to generate the corresponding (R)DTBM-SEGPHOS·AgOCH2CF3, which is considered to be the true catalyst in the present asymmetric α-amination reaction. Subsequently, the thus generated chiral silver alkoxide attacks alkenyl trifluoroacetate 1 to yield chiral silver enolate 4 accompanied by 2,2,2-trifluoroethyl trifluoroacetate. Then, chiral silver enolate 4 undergoes amination with azo diester 2 to afford chiral silver amide of α-hydrazino ketone 5. Finally, protonation of chiral silver amide 5 with CF3CH2OH results in the formation of enantiomerically enriched α-amino ketone 3
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Fig. 1 Plausible catalytic mechanism for the asymmetric α-amination reaction catalyzed by chiral silver alkoxide.
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Fig. 2 A hypothesis for enantioface discrimination between an azo diester and a silver enolate.
and the regeneration of the chiral silver alkoxide. The rapid alcoholysis of silver amide 5 is the key to success in the efficient catalytic cycle. The proposed transition state structures of this catalytic enantioselective α-amination are exhibited in Fig. 2. An azo diester approaches the α-carbon atom of a chiral silver enolate to avoid steric repulsion from a bulky aryl group of (R)DTBM-SEGPHOS. Accordingly, amination takes place selectively at the Re face of the silver enolate to provide the (R)α-amino ketone.
Conclusions We have developed a novel catalytic asymmetric α-amination reaction. The use of in situ generated chiral silver alkoxide as the chiral catalyst allows the synthesis of various optically active α-hydrazino ketones with enantioselectivities of up to 97% ee. The catalytic cycle through a chiral silver enolate offers an alternative asymmetric C–N bond forming process. To the best of our knowledge, this is the first example of the enantioselective α-amination catalyzed by a chiral silver alkoxide. Further studies of the extension of the present silver catalytic system to other asymmetric reactions are underway.
Experimental General methods Infrared (IR) spectra were recorded on a JASCO FT/IR-4100 using ATR. NMR spectra were recorded on a JEOL JNM LA-400 (400 MHz for 1H NMR and 100 MHz for 13C NMR, Chemical Analysis Center, Chiba University) or a LA-500 spectrometer (500 MHz for 1H NMR and 125.65 MHz for 13C NMR, Chemical Analysis Center, Chiba University). Chemical shifts were reported in ppm on the δ scale relative to Me4Si (δ = 0 for 1 H NMR) and CDCl3 (δ = 77.0 for 13C NMR) as an internal reference. ESI mass spectra were measured on a Thermo Scientific Exactive (Chemical Analysis Center, Chiba University). Optical rotations were measured on a JASCO P-1020 polarimeter. Column chromatography was conducted with silica gel 60 N (Kanto Chemical, spherical, neutral, 63–230 μm). Analytical TLC was done on precoated (0.25 mm) silica gel plates. The enantiomeric excesses were determined by HPLC. HPLC analysis was performed on JASCO HPLC
1938 | Org. Biomol. Chem., 2014, 12, 1935–1941
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systems containing the following instruments: a pump, PU-2080; a detector, UV-2075, measured at 254 nm; a column, Daicel Chiralcel OD-H or Daicel Chiralpak AD-H or AD-3. All experiments were carried out under an atmosphere of standard grade argon gas. THF was freshly distilled over sodium benzophenone ketyl under argon gas. (R)-SEGPHOS, (R)-DM-SEGPHOS and (R)-DTBM-SEGPHOS were donated by Takasago International Corporation. (R,R)-t-Bu-QuinoxP* was donated by Nippon Chemical Industrial Co., Ltd. Alkenyl trifluoroacetates were prepared by treating the corresponding ketones with trifluoroacetic anhydride and purified by column chromatography on silica gel and subsequent distillation before use.8b Other chemicals were used as purchased. General experimental procedure for catalytic asymmetric α-amination reaction catalysed by (R)-DTBM-SEGPHOS·AgOTf (Tables 2 and 3) A mixture of AgOTf (2.56 mg, 0.01 mmol) and (R)-DTBM-SEGPHOS (11.8 mg, 0.01 mmol) was dissolved in a mixture of dry THF (2.5 mL) and dry DMF (0.5 mL) under an argon atmosphere and with direct light excluded, and stirred at room temperature for 20 min. To the resulting solution was added CF3CH2OH (718 μL, 10 mmol) at −78 °C and the mixture was stirred at this temperature for 5 min. Then alkenyl trifluoroacetate (0.6 mmol) and azo diester (0.5 mmol) were successively added to the solution at −78 °C. After being stirred for 11–24 h at this temperature, azo diester was completely consumed. The reaction mixture was concentrated in vacuo and the residual crude product was purified by column chromatography on silica gel to give the corresponding α-hydrazino ketone. The enantiomeric ratio was determined by HPLC analysis. Dimethyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3aa, >99% yield, white solid, Table 2, entry 1; Table 3, entry 2). 1H NMR (500 MHz, CDCl3) δ 8.00 (d, 1H, J = 7.7 Hz, Ar-H), 7.50 (t, 1H, J = 7.5 Hz, Ar-H), 7.30 (m, 1H, Ar-H), 7.25 (d, 1H, J = 7.4 Hz, Ar-H), 7.07–6.74 (m, 1H, NH), 5.22–4.96 (m, 1H, CH), 3.79 (s, 3H, CH3), 3.74 (s, 3H, CH3), 3.24 (m, one proton of CH2), 3.06 (m, one proton of CH2), 2.54–2.26 (m, 2H, CH2); 13C NMR (125.76 MHz, CDCl3) δ 194.6, 194.4, 157.4, 156.9, 156.6, 143.7, 134.0, 131.7, 131.6, 128.7, 127.6, 126.7, 65.3, 64.5, 53.8, 52.8, 28.7, 27.6, 27.4, 22.5, 14.0; IR (neat) 3272, 2956, 1757, 1722, 1681, 1601, 1518, 1440, 1229, 1065, 763 cm−1; MS (ESI) exact mass calcd for [C14H16O5N2Na]+ ([M + Na]+): 315.0951, found: 315.0943; [α]23.6 +14.5° (c 0.75, CHCl3, 95% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 28.5 min (major), t2 = 38.7 min (minor); Mp 162–168 °C. (R)-Diethyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ab, >99% yield, Table 2, entry 2).9 1H NMR (500 MHz, CDCl3) δ 8.01 (d, 1H, J = 7.1 Hz, Ar-H), 7.50 (m, 1H, Ar-H), 7.31 (m, 1H, Ar-H), 7.25 (d, 1H, J = 6.9 Hz, Ar-H), 6.95–6.66 (m, 1H, NH), 5.21–4.95 (m, 1H, CH), 4.23–4.19 (m, 4H, 2CH2), 3.27–3.21 (m, 1H, one proton of CH2), 3.07–3.04 (m, 1H, one proton of CH2), 2.53–2.29 (m, 2H, CH2), 1.30–1.24 (m, 6H, 2CH3); 13C NMR (125.76 MHz, CDCl3) δ 194.6, 194.3, 156.9, 156.5, 156.34, 156.25, 143.7, 133.9, 131.8,
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131.6, 128.6, 127.5, 126.6, 65.2, 64.2, 62.8, 62.6, 61.8, 61.7, 28.6, 27.6, 27.4, 14.2; IR (neat) 3676, 3009, 1714, 1688, 1601, 1413, 1257, 1089 cm−1; MS (ESI) exact mass calcd for [C16H20O5N2Na]+ ([M + Na]+): 343.1264, found: 343.1252; [α]23.7 +7.45° (c 1.0, CHCl3, 90% ee); [α]25.2 −5.73° (c 1.0, EtOH, D D 90% ee) [lit.;9 [α]20 D +4.1° (c 0.25, EtOH, 90% ee, (S)-isomer)]; HPLC (Daicel Chiralcel OD-H × 2, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) tR = 38.6 min (major), tS = 45.2 min (minor); Mp 118–120 °C. Diisopropyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ac, >99% yield, white solid, Table 2, entry 3; Table 3, entry 3). 1H NMR (400 MHz, CDCl3) δ 8.01 (d, 1H, J = 7.7 Hz, Ar-H), 7.50 (m, 1H, Ar-H), 7.32 (m, 1H, Ar-H), 7.25 (m, 1H, Ar-H), 6.59–6.40 (m, 1H, NH), 5.20–4.96 (m, 3H, 3CH) 3.30–3.21 (m, 1H, one proton of CH2), 3.09–3.05 (m, 1H, one proton of CH2), 2.55–2.29 (m, 2H, CH2), 1.32–1.21 (m, 12H, 4CH3); 13C NMR (99.54 MHz, CDCl3) δ 194.8, 194.6, 156.7, 156.1, 143.8, 134.0, 131.9, 128.7, 127.6, 126.7, 70.9, 70.5, 69.6, 69.4, 65.4, 64.1, 28.8, 27.7, 27.5, 22.0, 21.9; IR (neat) 3280, 3249, 2980, 2937, 1749, 1712, 1681, 1601, 1513, 1414, 1308, 1234 cm−1; MS (ESI) exact mass calcd for [C18H24O5N2Na]+ ([M + Na]+): 371.1577, found: 371.1568; [α]23.4 +7.85° (c 0.5, CHCl3, 97% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 9.1 min (minor), t2 = 10.7 min (major); Mp 147–151 °C. Dibenzyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ae, 86% yield, white solid, Table 2, entry 5).6,11 1H NMR (500 MHz, CDCl3) δ 7.99 (d, 1H, J = 7.8 Hz, Ar-H), 7.49 (m, 1H, Ar-H), 7.32–7.25 (m, 12H, Ar-H), 6.94–6.65 (m, 1H, NH), 5.20–4.95 (m, 5H, CH and 2CH2) 3.27–3.18 (m, 1H, one proton of CH2), 3.07–3.04 (m, 1H, one proton of CH2), 2.57–2.55 (m, 1H, one proton of CH2), 2.33–2.31 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 194.6, 194.3, 156.8, 156.6, 156.2, 143.75, 143.68, 135.7, 135.5, 134.1, 131.8, 128.8, 128.5, 128.3, 128.1, 128.0, 127.7, 127.5, 126.8, 68.7, 68.3, 67.7, 67.6, 65.5, 64.5, 28.7, 27.7, 27.5; IR (neat) 3676, 3268, 3009, 1712, 1693, 1604, 1455, 1415, 1242, 1089 cm−1; MS (ESI) exact mass calcd for [C26H24O5N2Na]+ ([M + Na]+): 467.1577, found: 467.1565; [α]23.9 −0.88° (c 0.5, CHCl3, 92% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.5 mL min−1) t1 = 49.7 min (major), t2 = 105.3 min (minor); Mp 109–111 °C. Dimethyl 1-(1-oxo-2,3-dihydro-1H-inden-2-yl)hydrazine-1,2dicarboxylate (3ba, >99% yield, white solid, Table 3, entry 1). 1H NMR (400 MHz, CDCl3) δ 7.75 (d, 1H, J = 7.7 Hz, Ar-H), 7.63 (t, 1H, J = 7.4 Hz, Ar-H), 7.47–7.35 (br, 1H, NH), 7.46 (d, 1H, J = 7.7 Hz, Ar-H), 7.38 (t, 1H, J = 7.4 Hz, Ar-H), 5.00 (brs, 1H, CH), 3.76 (s, 3H, CH3), 3.72 (s, 3H, CH3), 3.56 (dd, 1H, J = 8.2, 17.2 Hz, one proton of CH2), 3.37 (dd, 1H, J = 3.4, 16.7 Hz, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 201.4, 157.2, 156.6, 156.1, 151.7, 135.5, 134.4, 127.6, 126.5, 124.1, 64.7, 54.4, 53.7, 52.8, 30.4; IR (neat) 3232, 2960, 1757, 1726, 1697, 1608, 1525, 1454, 1393, 1285, 1243, 1068 cm−1; MS (ESI) exact mass calcd for [C13H14O5N2Na]+ ([M + Na]+): 301.0795, found: 301.0789; [α]23.9 +52.3° (c 0.24, CHCl3, 71% ee); HPLC D (Daicel Chiralcel OD-H, hexane–i-PrOH = 9/1, flow rate =
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1.0 mL min−1) t1 = 34.6 min (major), t2 = 55.9 min (minor); Mp 163–167 °C. Dimethyl 1-(5-oxo-6,7,8,9-tetrahydro-5H-benzo[7]annulen-6yl)hydrazine-1,2-dicarboxylate (3ca, >99% yield, white solid, Table 3, entry 4). 1H NMR (400 MHz, CDCl3) δ 7.85 (d, 1H, J = 7.8 Hz, Ar-H), 7.45 (m, 1H, Ar-H), 7.32 (m, 1H, Ar-H), 7.24 (d, 1H, J = 7.5 Hz, Ar-H), 6.94–6.69 (m, 1H, NH), 5.26–5.03 (m, 1H, CH), 3.78–3.74 (m, 6H, 2CH3), 3.12–3.07 (m, 1H, one proton of CH2), 2.98–2.93 (m, 1H, one proton of CH2), 2.35 (brs, 1H, one proton of CH2), 2.21 (brs, 1H, one proton of CH2), 1.94 (m, 1H, one proton of CH2), 1.79 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 201.8, 201.4, 157.4, 157.1, 156.6, 142.5, 142.1, 135.9, 132.9, 130.2, 129.4, 128.5, 126.7, 66.4, 65.6, 60.3, 54.6, 53.8, 53.6, 53.1, 52.8, 33.6, 25.9, 25.7, 23.7, 20.9; IR (neat) 3299, 2959, 1731, 1666, 1596, 1515, 1441, 1255, 1225, 1068, 736 cm−1; MS (ESI) exact mass calcd for [C15H18O5N2Na]+ ([M + Na]+): 329.1108, found: 329.1097; [α]24.3 −5.3° (c 1.0, CHCl3, D 96% ee); HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 9/1, flow rate = 1.0 mL min−1) t1 = 42.2 min (major), t2 = 57.5 min (minor); Mp 117–120 °C. Dimethyl 1-(6-methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen2-yl)hydrazine-1,2-dicarboxylate (3da, >99% yield, white solid, Table 3, entry 5). 1H NMR (400 MHz, CDCl3) δ 7.98 (d, 1H, J = 8.9 Hz, Ar-H), 6.84 (dd, 1H, J = 2.0, 8.8 Hz, Ar-H), 6.79–6.51 (m, 1H, NH), 6.70 (s, 1H, Ar-H), 5.17–4.90 (m, 1H, CH), 3.86 (s, 3H, CH3), 3.80 (s, 3H, CH3), 3.73 (s, 3H, CH3), 3.21 (m, 1H, one proton of, CH2), 3.01 (d, 1H, J = 16.7 Hz, one proton of CH2), 2.49 (m, 1H, one proton of CH2), 2.29 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 193.1, 164.1, 157.4, 157.0, 156.6, 146.3, 130.1, 125.3, 113.5, 112.4, 65.1, 64.3, 55.4, 54.6, 53.7, 52.8, 29.0, 27.5; IR (neat) 3245, 2972, 2901, 1747, 1713, 1666, 1602, 1522, 1445, 1355, 1288, 1266, 1234 cm−1; MS (ESI) exact mass calcd for [C15H18O6N2Na]+ ([M + Na]+): 345.1057, found: 345.1048; [α]24.1 +3.9° (c 1.0, CHCl3, 80% ee); HPLC (Daicel Chiralpak AD-H D and AD-3, hexane–i-PrOH = 3/1, flow rate = 1.0 mL min−1) t1 = 41.0 min (major), t2 = 46.8 min (minor); Mp 175–179 °C. Diisopropyl 1-(6-methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3dc, >99% yield, white solid, Table 3, entry 6). 1H NMR (500 MHz, CDCl3) δ 7.98 (d, 1H, J = 8.9 Hz, Ar-H), 6.83 (d, 1H, J = 6.6 Hz, Ar-H), 6.69 (s, 1H, Ar-H), 6.57–6.36 (m, 1H, NH), 5.15–4.85 (m, 3H, 3CH), 3.86 (s, 3H, CH3), 3.21 (m, 1H, one proton of CH2), 3.01 (d, 1H, J = 16.6 Hz, one proton of CH2), 2.51–2.25 (m, 2H, CH2), 1.32–1.21 (m, 12H, 4CH3); 13C NMR (125.76 MHz, CDCl3) δ 193.3, 192.9, 164.0, 156.6, 156.4, 156.0, 146.3, 146.0, 130.0, 125.5, 113.4, 112.4, 70.8, 70.4, 69.5, 69.3, 65.1, 63.8, 55.4, 29.1, 27.7, 27.5, 22.0, 21.9, 21.7; IR (neat) 3674, 3281, 2968, 2900, 1749, 1719, 1675, 1600, 1514, 1369, 1253, 1112 cm−1; MS (ESI) exact mass calcd for [C19H26O6N2Na]+ ([M + Na]+): 401.1683, found: 401.1667; [α]24.7 −8.58° (c 1.0, CHCl3, 96% ee); HPLC (Daicel Chiralcel D OD-H, hexane/i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 12.0 min (minor), t2 = 14.7 min (major); Mp 125–130 °C. Dimethyl 1-(6-methoxy-2-methyl-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ea, >99% yield, white solid, Table 3, entry 7). 1H NMR (500 MHz, CDCl3) δ 8.05 (d, 1H, J = 8.6 Hz, Ar-H), 7.39–7.07 (m, 1H, NH), 6.84 (dd, 1H,
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J = 8.9, 2.3 Hz, Ar-H), 6.68 (m, 1H, Ar-H), 3.85 (s, 3H, CH3), 3.78 (s, 3H, CH3), 3.65 (brs, 3H, CH3), 3.05–2.88 (m, 3H, CH2 and one proton of CH2), 2.29–2.14 (m, 1H, one proton of CH2), 1.42 (s, 3H, CH3); 13C NMR (125.76 MHz, CDCl3) δ 195.2, 163.7, 157.3, 155.4, 144.8, 130.7, 124.6, 113.5, 112.2, 66.9, 55.3, 53.2, 52.9, 33.0, 27.0, 19.9; IR (neat) 3675, 3308, 3005, 1743, 1716, 1677, 1601, 1520, 1440, 1409, 1394, 1382, 1262, 1106, 1084 cm−1; MS (ESI) exact mass calcd for [C16H20O6N2Na]+ ([M + Na]+): 359.1214, found: 359.1203; [α]24.5 −4.82° (c 1.0, CHCl3, 30% D ee); HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 9/1, flow rate = 1.0 mL min−1) t1 = 17.4 min (major), t2 = 41.3 min (minor); Mp 118–128 °C. (S)-Diethyl 1-(1-oxo-1-phenylpropan-2-yl)hydrazine-1,2-dicarboxylate (3fb, >99% yield, white solid, Table 3, entry 8).3g,9 1H NMR (500 MHz, CDCl3) δ 7.92 (m, 2H, Ar-H), 7.59 (m, 1H, ArH), 7.48 (t, 2H, J = 6.9 Hz, Ar-H), 6.85–6.63 (m, 1H, NH), 5.83–5.65 (m, 1H, CH), 4.22–4.17 (m, 4H, 2CH2), 1.48 (d, 3H, J = 6.1 Hz, CH3), 1.29–1.16 (m, 6H, 2CH3); 13C NMR (99.54 MHz, CDCl3) δ 200.5, 199.9, 156.9, 156.4, 156.3, 156.0, 134.6, 133.6, 128.7, 128.4, 128.2, 62.8, 61.8, 59.0, 58.0, 27.8, 26.8, 17.4, 14.9, 14.4, 14.3, 13.5; IR (neat) 3675, 3308, 3007, 1714, 1691, 1597, 1452, 1414, 1254, 1088 cm−1; MS (ESI) exact mass calcd for [C15H21O5N2]+ ([M + H]+): 309.1445, found: 309.1442; [α]20.8 +6.0° (c 1.0, CHCl3, 17% ee) [lit.;9 [α]20 D D +38.6° (c 0.58, CHCl3, 94% ee, (S)-isomer)]; HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 3/1, flow rate = 1.0 mL min−1) tR = 9.2 min (minor), tS = 11.7 min (major); Mp 64–66 °C. Dimethyl 1-(1-oxo-1-phenylpentan-2-yl)hydrazine-1,2-dicarboxylate (3ga, >99% yield, white solid, Table 3, entry 9). 1H NMR (400 MHz, CDCl3) δ 7.92 (m, 2H, Ar-H), 7.60 (t, 1H, J = 7.2 Hz, Ar-H), 7.49 (t, 2H, J = 7.6 Hz, Ar-H), 7.05–6.89 (m, 1H, NH), 5.77–5.55 (m, 1H, CH), 3.76 (s, 6H, 2CH3), 1.78–1.49 (m, 4H, 2CH2), 0.96 (t, 3H, J = 7.2 H, CH3); 13C NMR (99.54 MHz, CDCl3) δ 200.9, 200.8, 157.5, 157.0, 156.3, 135.1, 133.7, 128.8, 128.4, 63.2, 62.2, 53.9, 52.9, 31.0, 30.7, 19.7, 13.8; IR (neat) 3277, 2954, 1754, 1678, 1530, 1448, 1394, 1247, 1208, 1065, 760 cm−1; MS (ESI) exact mass calcd for [C15H21O5N2]+ ([M + H]+): 309.1445, found: 309.1438; [α]21.0 +16.4° (c 0.5, D CHCl3, 31% ee); HPLC (Daicel Chiralcel OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 10.8 min (major), t2 = 12.0 min (minor); Mp 78–82 °C.
Acknowledgements This work was supported by MEXT/JSPS KAKENHI grant number 25410107, The Naito Foundation, and The COE Startup Program in Chiba University led by Professor Takayoshi Arai. We gratefully acknowledge the generous gift of (R)-SEGPHOS, (R)-DM-SEGPHOS, and (R)-DTBM-SEGPHOS from Takasago International Corporation and (R,R)-t-BuQuinoxP* from Nippon Chemical Industrial Co., Ltd.
Notes and references 1 (a) R. O. Duthaler, Angew. Chem., Int. Ed., 2003, 42, 975; (b) C. Greck, B. Drouillat and C. Thomassigny, Eur. J. Org.
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Asymmetric α-amination reaction of alkenyl trifluoroacetates catalyzed by a chiral phosphine–silver complex† Akira Yanagisawa,* Ryoji Miyake and Kazuhiro Yoshida
Received 23rd October 2013, Accepted 21st January 2014
The asymmetric α-amination of alkenyl trifluoroacetates with dialkyl azodicarboxylates catalyzed by the
DOI: 10.1039/c3ob42111b
DTBM-SEGPHOS·AgOTf complex takes place in the presence of 2,2,2-trifluoroethanol with almost
www.rsc.org/obc
quantitative yield and high ees of up to 97%.
Introduction The catalytic asymmetric α-amination reaction of carbonyl compounds is a beneficial way to form optically active α-amino carbonyl compounds, including α-amino acids and their derivatives; the functional groups are often seen in natural products or pharmaceutical compounds.1 Since the first report of the catalytic enantioselective α-amination of carbonyl compounds using azodicarboxylates as the electrophilic nitrogen source by Evans and Nelson in 1997,2 various methods that employ chiral catalysts have emerged, affording such α-aminated products in high yields and satisfactory optical purities.3,4 In the case of chiral metal complex catalyzed asymmetric transformations via chiral metal enolates, however, most of the protocols use readily enolizable carbonyl compounds as substrates,2,3b,c and as far as we know, there is no example of the catalytic reaction via a chiral metal enolate derived from simple ketones. We report here a novel example of the enantioselective α-amination reaction of simple-ketonederived alkenyl trifluoroacetates with dialkyl azodicarboxylates using the DTBM-SEGPHOS·AgOTf complex as the asymmetric catalyst in the presence of 2,2,2-trifluoroethanol (Scheme 1). The reaction is assumed to proceed via a chiral silver enolate.
Scheme 1 Chiral-silver-catalyzed asymmetric α-amination reaction of alkenyl trifluoroacetates with dialkyl azodicarboxylates.
Department of Chemistry, Graduate School of Science, Chiba University, Inage, Chiba 263-8522, Japan. E-mail: [email protected]; Fax: +81-(0)43-290-2789; Tel: +81-(0)43-290-2789 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ob42111b
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Results and discussion Kobayashi et al. reported that silver salts catalyzed the amination of silyl enol ethers with azo diester compounds.5 An asymmetric version of this reaction was achieved by the same group using BINAP as the chiral ligand.6 In contrast, we found that a chiral phosphine–silver(I) complex acted as the chiral cocatalyst in the asymmetric α-aminooxylation (O-nitroso aldol reaction) of alkenyl trichloroacetates with nitrosoarenes catalyzed by dibutyltin dimethoxide.7 The reaction took place through a tin enolate and the tin dimethoxide was regenerated in the presence of MeOH. In addition, the chiral phosphine– silver(I) complex was considered to activate a nitrosoarene through its coordination to the nitrogen atom. We envisioned that if azo diester compounds could be applied instead of nitrosoarenes to the dual catalyst system, the asymmetric α-amination of alkenyl esters would be possible. Thus, we investigated the suitability of an azo diester as an electrophile for the reaction. When a 1.2 : 1 mixture of alkenyl trifluoroacetate 1a8 and dimethyl azodicarboxylate (2a) was treated with (R)-DTBM-SEGPHOS (6 mol%), AgOTf (5 mol%), and Bu2Sn(OMe)2 (20 mol%) in the presence of MeOH (5 equiv.) and CF3CH2OH (10 equiv.) in THF at −40 °C for 2 h, targeted product 3aa was obtained quantitatively with 69% ee (Table 1, entry 1). Then, we studied the additive effect of a tertiary amine on the enantioselectivity and found that the enantiomeric excess of 3aa increased to 86% in the presence of 5 mol% of N,N-dimethylaniline (entry 2). The presence of Bu2Sn(OMe)2 is not necessary for the present catalytic system; for instance, the reaction proceeded smoothly in the absence of this catalyst at −40 °C to give the desired α-aminated product 3aa without significantly decreasing its ee (entry 3 vs. entry 2). Then, we screened for chiral phosphine ligands and found that DTBM-SEGPHOS was the ligand of choice (entries 3–7). As an additional optimization trial, we examined the solvent effect without PhNMe2 (entries 8–11) and found that the use of
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Table 1
Organic & Biomolecular Chemistry Optimization of the reaction conditions
Entry
Chiral phosphine
x
y
z
Solvent
T (°C)
Time (h)
Yielda (%)
eeb (%)
1c 2c,d 3d,e 4d 5d 6d 7d 8 9 10 11 12 13 14 15 16 17
(R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (S)-BINAP (R)-SEGPHOS (R)-DM-SEGPHOS (R,R)-t-Bu-QuinoxP* (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS (R)-DTBM-SEGPHOS
6 6 6 6 6 6 6 6 6 6 6 5 5 2 2 2 2
5 5 5 5 5 5 5 5 5 5 5 5 5 2 2 2 2
10 10 10 10 10 10 10 10 10 10 10 10 20 20 20 20 —
THF THF THF THF THF THF THF THF DMF THF–DMF (1 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF–DMF (5 : 1) THF DMF CF3CH2OH
−40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −40 −78 −78 −78 −78 −40
2 1 2 20 20 20 20 1 1 1 1 1 15 15 42 30 24
>99 >99 >99 60 70 52 14 >99 >99 >99 >99 >99 >99 >99 70 >99 40
69 86 85 41 11 60 14 81 76 90 91 92 95 95 93 82 99 >99 >99 99
71
Me i-Pr
15 11
3aa 3ac
>99 >99
95 97
2a
Me
16
3ca
>99
96
5 6
2a 2c
Me i-Pr
11 16
3da 3dc
>99 >99
90 96
7
2a
Me
15
3ca
>99
30
8
2b
Et
18
3fb
>99
17 (S)c
9
2a
Me
21
3ga
>99
31
Time (h)
Me
2a 2c
4
Azo diester
R
1
2a
2 3
Entry
a
Alkenyl ester
4
Isolated yield. b Determined by HPLC analysis. c The absolute configuration is shown in parentheses.
and 6). The reaction of acyclic alkenyl trifluoroacetate 1f (E/Z = 1/9) with azo diester 2b also furnished an α-aminated product in an almost quantitative yield under the standard reaction conditions, but the optical purity (17% ee) was low (entry 8). Substitution of the methyl group of 1f with n-propyl group raised the enantioselectivity (entry 9). A plausible catalytic cycle is shown in Fig. 1. First, (R)DTBM-SEGPHOS·AgOTf reacts with 2,2,2-trifluoroethanol10 in the presence of an appropriate amine, such as azo diester 2 or α-aminated product 3, to generate the corresponding (R)DTBM-SEGPHOS·AgOCH2CF3, which is considered to be the true catalyst in the present asymmetric α-amination reaction. Subsequently, the thus generated chiral silver alkoxide attacks alkenyl trifluoroacetate 1 to yield chiral silver enolate 4 accompanied by 2,2,2-trifluoroethyl trifluoroacetate. Then, chiral silver enolate 4 undergoes amination with azo diester 2 to afford chiral silver amide of α-hydrazino ketone 5. Finally, protonation of chiral silver amide 5 with CF3CH2OH results in the formation of enantiomerically enriched α-amino ketone 3
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Fig. 1 Plausible catalytic mechanism for the asymmetric α-amination reaction catalyzed by chiral silver alkoxide.
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Fig. 2 A hypothesis for enantioface discrimination between an azo diester and a silver enolate.
and the regeneration of the chiral silver alkoxide. The rapid alcoholysis of silver amide 5 is the key to success in the efficient catalytic cycle. The proposed transition state structures of this catalytic enantioselective α-amination are exhibited in Fig. 2. An azo diester approaches the α-carbon atom of a chiral silver enolate to avoid steric repulsion from a bulky aryl group of (R)DTBM-SEGPHOS. Accordingly, amination takes place selectively at the Re face of the silver enolate to provide the (R)α-amino ketone.
Conclusions We have developed a novel catalytic asymmetric α-amination reaction. The use of in situ generated chiral silver alkoxide as the chiral catalyst allows the synthesis of various optically active α-hydrazino ketones with enantioselectivities of up to 97% ee. The catalytic cycle through a chiral silver enolate offers an alternative asymmetric C–N bond forming process. To the best of our knowledge, this is the first example of the enantioselective α-amination catalyzed by a chiral silver alkoxide. Further studies of the extension of the present silver catalytic system to other asymmetric reactions are underway.
Experimental General methods Infrared (IR) spectra were recorded on a JASCO FT/IR-4100 using ATR. NMR spectra were recorded on a JEOL JNM LA-400 (400 MHz for 1H NMR and 100 MHz for 13C NMR, Chemical Analysis Center, Chiba University) or a LA-500 spectrometer (500 MHz for 1H NMR and 125.65 MHz for 13C NMR, Chemical Analysis Center, Chiba University). Chemical shifts were reported in ppm on the δ scale relative to Me4Si (δ = 0 for 1 H NMR) and CDCl3 (δ = 77.0 for 13C NMR) as an internal reference. ESI mass spectra were measured on a Thermo Scientific Exactive (Chemical Analysis Center, Chiba University). Optical rotations were measured on a JASCO P-1020 polarimeter. Column chromatography was conducted with silica gel 60 N (Kanto Chemical, spherical, neutral, 63–230 μm). Analytical TLC was done on precoated (0.25 mm) silica gel plates. The enantiomeric excesses were determined by HPLC. HPLC analysis was performed on JASCO HPLC
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systems containing the following instruments: a pump, PU-2080; a detector, UV-2075, measured at 254 nm; a column, Daicel Chiralcel OD-H or Daicel Chiralpak AD-H or AD-3. All experiments were carried out under an atmosphere of standard grade argon gas. THF was freshly distilled over sodium benzophenone ketyl under argon gas. (R)-SEGPHOS, (R)-DM-SEGPHOS and (R)-DTBM-SEGPHOS were donated by Takasago International Corporation. (R,R)-t-Bu-QuinoxP* was donated by Nippon Chemical Industrial Co., Ltd. Alkenyl trifluoroacetates were prepared by treating the corresponding ketones with trifluoroacetic anhydride and purified by column chromatography on silica gel and subsequent distillation before use.8b Other chemicals were used as purchased. General experimental procedure for catalytic asymmetric α-amination reaction catalysed by (R)-DTBM-SEGPHOS·AgOTf (Tables 2 and 3) A mixture of AgOTf (2.56 mg, 0.01 mmol) and (R)-DTBM-SEGPHOS (11.8 mg, 0.01 mmol) was dissolved in a mixture of dry THF (2.5 mL) and dry DMF (0.5 mL) under an argon atmosphere and with direct light excluded, and stirred at room temperature for 20 min. To the resulting solution was added CF3CH2OH (718 μL, 10 mmol) at −78 °C and the mixture was stirred at this temperature for 5 min. Then alkenyl trifluoroacetate (0.6 mmol) and azo diester (0.5 mmol) were successively added to the solution at −78 °C. After being stirred for 11–24 h at this temperature, azo diester was completely consumed. The reaction mixture was concentrated in vacuo and the residual crude product was purified by column chromatography on silica gel to give the corresponding α-hydrazino ketone. The enantiomeric ratio was determined by HPLC analysis. Dimethyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3aa, >99% yield, white solid, Table 2, entry 1; Table 3, entry 2). 1H NMR (500 MHz, CDCl3) δ 8.00 (d, 1H, J = 7.7 Hz, Ar-H), 7.50 (t, 1H, J = 7.5 Hz, Ar-H), 7.30 (m, 1H, Ar-H), 7.25 (d, 1H, J = 7.4 Hz, Ar-H), 7.07–6.74 (m, 1H, NH), 5.22–4.96 (m, 1H, CH), 3.79 (s, 3H, CH3), 3.74 (s, 3H, CH3), 3.24 (m, one proton of CH2), 3.06 (m, one proton of CH2), 2.54–2.26 (m, 2H, CH2); 13C NMR (125.76 MHz, CDCl3) δ 194.6, 194.4, 157.4, 156.9, 156.6, 143.7, 134.0, 131.7, 131.6, 128.7, 127.6, 126.7, 65.3, 64.5, 53.8, 52.8, 28.7, 27.6, 27.4, 22.5, 14.0; IR (neat) 3272, 2956, 1757, 1722, 1681, 1601, 1518, 1440, 1229, 1065, 763 cm−1; MS (ESI) exact mass calcd for [C14H16O5N2Na]+ ([M + Na]+): 315.0951, found: 315.0943; [α]23.6 +14.5° (c 0.75, CHCl3, 95% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 28.5 min (major), t2 = 38.7 min (minor); Mp 162–168 °C. (R)-Diethyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ab, >99% yield, Table 2, entry 2).9 1H NMR (500 MHz, CDCl3) δ 8.01 (d, 1H, J = 7.1 Hz, Ar-H), 7.50 (m, 1H, Ar-H), 7.31 (m, 1H, Ar-H), 7.25 (d, 1H, J = 6.9 Hz, Ar-H), 6.95–6.66 (m, 1H, NH), 5.21–4.95 (m, 1H, CH), 4.23–4.19 (m, 4H, 2CH2), 3.27–3.21 (m, 1H, one proton of CH2), 3.07–3.04 (m, 1H, one proton of CH2), 2.53–2.29 (m, 2H, CH2), 1.30–1.24 (m, 6H, 2CH3); 13C NMR (125.76 MHz, CDCl3) δ 194.6, 194.3, 156.9, 156.5, 156.34, 156.25, 143.7, 133.9, 131.8,
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131.6, 128.6, 127.5, 126.6, 65.2, 64.2, 62.8, 62.6, 61.8, 61.7, 28.6, 27.6, 27.4, 14.2; IR (neat) 3676, 3009, 1714, 1688, 1601, 1413, 1257, 1089 cm−1; MS (ESI) exact mass calcd for [C16H20O5N2Na]+ ([M + Na]+): 343.1264, found: 343.1252; [α]23.7 +7.45° (c 1.0, CHCl3, 90% ee); [α]25.2 −5.73° (c 1.0, EtOH, D D 90% ee) [lit.;9 [α]20 D +4.1° (c 0.25, EtOH, 90% ee, (S)-isomer)]; HPLC (Daicel Chiralcel OD-H × 2, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) tR = 38.6 min (major), tS = 45.2 min (minor); Mp 118–120 °C. Diisopropyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ac, >99% yield, white solid, Table 2, entry 3; Table 3, entry 3). 1H NMR (400 MHz, CDCl3) δ 8.01 (d, 1H, J = 7.7 Hz, Ar-H), 7.50 (m, 1H, Ar-H), 7.32 (m, 1H, Ar-H), 7.25 (m, 1H, Ar-H), 6.59–6.40 (m, 1H, NH), 5.20–4.96 (m, 3H, 3CH) 3.30–3.21 (m, 1H, one proton of CH2), 3.09–3.05 (m, 1H, one proton of CH2), 2.55–2.29 (m, 2H, CH2), 1.32–1.21 (m, 12H, 4CH3); 13C NMR (99.54 MHz, CDCl3) δ 194.8, 194.6, 156.7, 156.1, 143.8, 134.0, 131.9, 128.7, 127.6, 126.7, 70.9, 70.5, 69.6, 69.4, 65.4, 64.1, 28.8, 27.7, 27.5, 22.0, 21.9; IR (neat) 3280, 3249, 2980, 2937, 1749, 1712, 1681, 1601, 1513, 1414, 1308, 1234 cm−1; MS (ESI) exact mass calcd for [C18H24O5N2Na]+ ([M + Na]+): 371.1577, found: 371.1568; [α]23.4 +7.85° (c 0.5, CHCl3, 97% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 9.1 min (minor), t2 = 10.7 min (major); Mp 147–151 °C. Dibenzyl 1-(1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ae, 86% yield, white solid, Table 2, entry 5).6,11 1H NMR (500 MHz, CDCl3) δ 7.99 (d, 1H, J = 7.8 Hz, Ar-H), 7.49 (m, 1H, Ar-H), 7.32–7.25 (m, 12H, Ar-H), 6.94–6.65 (m, 1H, NH), 5.20–4.95 (m, 5H, CH and 2CH2) 3.27–3.18 (m, 1H, one proton of CH2), 3.07–3.04 (m, 1H, one proton of CH2), 2.57–2.55 (m, 1H, one proton of CH2), 2.33–2.31 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 194.6, 194.3, 156.8, 156.6, 156.2, 143.75, 143.68, 135.7, 135.5, 134.1, 131.8, 128.8, 128.5, 128.3, 128.1, 128.0, 127.7, 127.5, 126.8, 68.7, 68.3, 67.7, 67.6, 65.5, 64.5, 28.7, 27.7, 27.5; IR (neat) 3676, 3268, 3009, 1712, 1693, 1604, 1455, 1415, 1242, 1089 cm−1; MS (ESI) exact mass calcd for [C26H24O5N2Na]+ ([M + Na]+): 467.1577, found: 467.1565; [α]23.9 −0.88° (c 0.5, CHCl3, 92% ee); HPLC (Daicel Chiralcel D OD-H, hexane–i-PrOH = 9/1, flow rate = 0.5 mL min−1) t1 = 49.7 min (major), t2 = 105.3 min (minor); Mp 109–111 °C. Dimethyl 1-(1-oxo-2,3-dihydro-1H-inden-2-yl)hydrazine-1,2dicarboxylate (3ba, >99% yield, white solid, Table 3, entry 1). 1H NMR (400 MHz, CDCl3) δ 7.75 (d, 1H, J = 7.7 Hz, Ar-H), 7.63 (t, 1H, J = 7.4 Hz, Ar-H), 7.47–7.35 (br, 1H, NH), 7.46 (d, 1H, J = 7.7 Hz, Ar-H), 7.38 (t, 1H, J = 7.4 Hz, Ar-H), 5.00 (brs, 1H, CH), 3.76 (s, 3H, CH3), 3.72 (s, 3H, CH3), 3.56 (dd, 1H, J = 8.2, 17.2 Hz, one proton of CH2), 3.37 (dd, 1H, J = 3.4, 16.7 Hz, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 201.4, 157.2, 156.6, 156.1, 151.7, 135.5, 134.4, 127.6, 126.5, 124.1, 64.7, 54.4, 53.7, 52.8, 30.4; IR (neat) 3232, 2960, 1757, 1726, 1697, 1608, 1525, 1454, 1393, 1285, 1243, 1068 cm−1; MS (ESI) exact mass calcd for [C13H14O5N2Na]+ ([M + Na]+): 301.0795, found: 301.0789; [α]23.9 +52.3° (c 0.24, CHCl3, 71% ee); HPLC D (Daicel Chiralcel OD-H, hexane–i-PrOH = 9/1, flow rate =
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1.0 mL min−1) t1 = 34.6 min (major), t2 = 55.9 min (minor); Mp 163–167 °C. Dimethyl 1-(5-oxo-6,7,8,9-tetrahydro-5H-benzo[7]annulen-6yl)hydrazine-1,2-dicarboxylate (3ca, >99% yield, white solid, Table 3, entry 4). 1H NMR (400 MHz, CDCl3) δ 7.85 (d, 1H, J = 7.8 Hz, Ar-H), 7.45 (m, 1H, Ar-H), 7.32 (m, 1H, Ar-H), 7.24 (d, 1H, J = 7.5 Hz, Ar-H), 6.94–6.69 (m, 1H, NH), 5.26–5.03 (m, 1H, CH), 3.78–3.74 (m, 6H, 2CH3), 3.12–3.07 (m, 1H, one proton of CH2), 2.98–2.93 (m, 1H, one proton of CH2), 2.35 (brs, 1H, one proton of CH2), 2.21 (brs, 1H, one proton of CH2), 1.94 (m, 1H, one proton of CH2), 1.79 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 201.8, 201.4, 157.4, 157.1, 156.6, 142.5, 142.1, 135.9, 132.9, 130.2, 129.4, 128.5, 126.7, 66.4, 65.6, 60.3, 54.6, 53.8, 53.6, 53.1, 52.8, 33.6, 25.9, 25.7, 23.7, 20.9; IR (neat) 3299, 2959, 1731, 1666, 1596, 1515, 1441, 1255, 1225, 1068, 736 cm−1; MS (ESI) exact mass calcd for [C15H18O5N2Na]+ ([M + Na]+): 329.1108, found: 329.1097; [α]24.3 −5.3° (c 1.0, CHCl3, D 96% ee); HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 9/1, flow rate = 1.0 mL min−1) t1 = 42.2 min (major), t2 = 57.5 min (minor); Mp 117–120 °C. Dimethyl 1-(6-methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen2-yl)hydrazine-1,2-dicarboxylate (3da, >99% yield, white solid, Table 3, entry 5). 1H NMR (400 MHz, CDCl3) δ 7.98 (d, 1H, J = 8.9 Hz, Ar-H), 6.84 (dd, 1H, J = 2.0, 8.8 Hz, Ar-H), 6.79–6.51 (m, 1H, NH), 6.70 (s, 1H, Ar-H), 5.17–4.90 (m, 1H, CH), 3.86 (s, 3H, CH3), 3.80 (s, 3H, CH3), 3.73 (s, 3H, CH3), 3.21 (m, 1H, one proton of, CH2), 3.01 (d, 1H, J = 16.7 Hz, one proton of CH2), 2.49 (m, 1H, one proton of CH2), 2.29 (m, 1H, one proton of CH2); 13C NMR (99.54 MHz, CDCl3) δ 193.1, 164.1, 157.4, 157.0, 156.6, 146.3, 130.1, 125.3, 113.5, 112.4, 65.1, 64.3, 55.4, 54.6, 53.7, 52.8, 29.0, 27.5; IR (neat) 3245, 2972, 2901, 1747, 1713, 1666, 1602, 1522, 1445, 1355, 1288, 1266, 1234 cm−1; MS (ESI) exact mass calcd for [C15H18O6N2Na]+ ([M + Na]+): 345.1057, found: 345.1048; [α]24.1 +3.9° (c 1.0, CHCl3, 80% ee); HPLC (Daicel Chiralpak AD-H D and AD-3, hexane–i-PrOH = 3/1, flow rate = 1.0 mL min−1) t1 = 41.0 min (major), t2 = 46.8 min (minor); Mp 175–179 °C. Diisopropyl 1-(6-methoxy-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3dc, >99% yield, white solid, Table 3, entry 6). 1H NMR (500 MHz, CDCl3) δ 7.98 (d, 1H, J = 8.9 Hz, Ar-H), 6.83 (d, 1H, J = 6.6 Hz, Ar-H), 6.69 (s, 1H, Ar-H), 6.57–6.36 (m, 1H, NH), 5.15–4.85 (m, 3H, 3CH), 3.86 (s, 3H, CH3), 3.21 (m, 1H, one proton of CH2), 3.01 (d, 1H, J = 16.6 Hz, one proton of CH2), 2.51–2.25 (m, 2H, CH2), 1.32–1.21 (m, 12H, 4CH3); 13C NMR (125.76 MHz, CDCl3) δ 193.3, 192.9, 164.0, 156.6, 156.4, 156.0, 146.3, 146.0, 130.0, 125.5, 113.4, 112.4, 70.8, 70.4, 69.5, 69.3, 65.1, 63.8, 55.4, 29.1, 27.7, 27.5, 22.0, 21.9, 21.7; IR (neat) 3674, 3281, 2968, 2900, 1749, 1719, 1675, 1600, 1514, 1369, 1253, 1112 cm−1; MS (ESI) exact mass calcd for [C19H26O6N2Na]+ ([M + Na]+): 401.1683, found: 401.1667; [α]24.7 −8.58° (c 1.0, CHCl3, 96% ee); HPLC (Daicel Chiralcel D OD-H, hexane/i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 12.0 min (minor), t2 = 14.7 min (major); Mp 125–130 °C. Dimethyl 1-(6-methoxy-2-methyl-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-1,2-dicarboxylate (3ea, >99% yield, white solid, Table 3, entry 7). 1H NMR (500 MHz, CDCl3) δ 8.05 (d, 1H, J = 8.6 Hz, Ar-H), 7.39–7.07 (m, 1H, NH), 6.84 (dd, 1H,
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J = 8.9, 2.3 Hz, Ar-H), 6.68 (m, 1H, Ar-H), 3.85 (s, 3H, CH3), 3.78 (s, 3H, CH3), 3.65 (brs, 3H, CH3), 3.05–2.88 (m, 3H, CH2 and one proton of CH2), 2.29–2.14 (m, 1H, one proton of CH2), 1.42 (s, 3H, CH3); 13C NMR (125.76 MHz, CDCl3) δ 195.2, 163.7, 157.3, 155.4, 144.8, 130.7, 124.6, 113.5, 112.2, 66.9, 55.3, 53.2, 52.9, 33.0, 27.0, 19.9; IR (neat) 3675, 3308, 3005, 1743, 1716, 1677, 1601, 1520, 1440, 1409, 1394, 1382, 1262, 1106, 1084 cm−1; MS (ESI) exact mass calcd for [C16H20O6N2Na]+ ([M + Na]+): 359.1214, found: 359.1203; [α]24.5 −4.82° (c 1.0, CHCl3, 30% D ee); HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 9/1, flow rate = 1.0 mL min−1) t1 = 17.4 min (major), t2 = 41.3 min (minor); Mp 118–128 °C. (S)-Diethyl 1-(1-oxo-1-phenylpropan-2-yl)hydrazine-1,2-dicarboxylate (3fb, >99% yield, white solid, Table 3, entry 8).3g,9 1H NMR (500 MHz, CDCl3) δ 7.92 (m, 2H, Ar-H), 7.59 (m, 1H, ArH), 7.48 (t, 2H, J = 6.9 Hz, Ar-H), 6.85–6.63 (m, 1H, NH), 5.83–5.65 (m, 1H, CH), 4.22–4.17 (m, 4H, 2CH2), 1.48 (d, 3H, J = 6.1 Hz, CH3), 1.29–1.16 (m, 6H, 2CH3); 13C NMR (99.54 MHz, CDCl3) δ 200.5, 199.9, 156.9, 156.4, 156.3, 156.0, 134.6, 133.6, 128.7, 128.4, 128.2, 62.8, 61.8, 59.0, 58.0, 27.8, 26.8, 17.4, 14.9, 14.4, 14.3, 13.5; IR (neat) 3675, 3308, 3007, 1714, 1691, 1597, 1452, 1414, 1254, 1088 cm−1; MS (ESI) exact mass calcd for [C15H21O5N2]+ ([M + H]+): 309.1445, found: 309.1442; [α]20.8 +6.0° (c 1.0, CHCl3, 17% ee) [lit.;9 [α]20 D D +38.6° (c 0.58, CHCl3, 94% ee, (S)-isomer)]; HPLC (Daicel Chiralpak AD-3, hexane–i-PrOH = 3/1, flow rate = 1.0 mL min−1) tR = 9.2 min (minor), tS = 11.7 min (major); Mp 64–66 °C. Dimethyl 1-(1-oxo-1-phenylpentan-2-yl)hydrazine-1,2-dicarboxylate (3ga, >99% yield, white solid, Table 3, entry 9). 1H NMR (400 MHz, CDCl3) δ 7.92 (m, 2H, Ar-H), 7.60 (t, 1H, J = 7.2 Hz, Ar-H), 7.49 (t, 2H, J = 7.6 Hz, Ar-H), 7.05–6.89 (m, 1H, NH), 5.77–5.55 (m, 1H, CH), 3.76 (s, 6H, 2CH3), 1.78–1.49 (m, 4H, 2CH2), 0.96 (t, 3H, J = 7.2 H, CH3); 13C NMR (99.54 MHz, CDCl3) δ 200.9, 200.8, 157.5, 157.0, 156.3, 135.1, 133.7, 128.8, 128.4, 63.2, 62.2, 53.9, 52.9, 31.0, 30.7, 19.7, 13.8; IR (neat) 3277, 2954, 1754, 1678, 1530, 1448, 1394, 1247, 1208, 1065, 760 cm−1; MS (ESI) exact mass calcd for [C15H21O5N2]+ ([M + H]+): 309.1445, found: 309.1438; [α]21.0 +16.4° (c 0.5, D CHCl3, 31% ee); HPLC (Daicel Chiralcel OD-H, hexane–i-PrOH = 9/1, flow rate = 0.7 mL min−1) t1 = 10.8 min (major), t2 = 12.0 min (minor); Mp 78–82 °C.
Acknowledgements This work was supported by MEXT/JSPS KAKENHI grant number 25410107, The Naito Foundation, and The COE Startup Program in Chiba University led by Professor Takayoshi Arai. We gratefully acknowledge the generous gift of (R)-SEGPHOS, (R)-DM-SEGPHOS, and (R)-DTBM-SEGPHOS from Takasago International Corporation and (R,R)-t-BuQuinoxP* from Nippon Chemical Industrial Co., Ltd.
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