Compound 6a

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InChIKey FZCFDZOISQWWFG-BVRKHOPBSA-N

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

A mixture of Rh₂(OAc)₄ (0.0025 mmol), imine 2b (0.3 mmol), indole 4a (0.25 mmol), 7b (0.005 mmol) and 4 Å MS (100 mg) in 2.0 mL toluene under an argon atmosphere was stirred at the -10°C. Diazo compound 3a (0.3 mmol) in 2.0 mL toluene was added over 1hr via a syringe pump. After the completion of the addition, the reaction was stirred at the -10°C for another 6hr and evaporated under reduced pressure to give the crude product. The crude product was purified by flash chromatography on silica gel (eluent: EtOAc/light petroleum ether = 1:100 ~ 1:40) to give the pure product 6a. White solid; mp: 145-148^oC; 94% yield; ¹H NMR (400MHz, CDCl₃): δ 7.36-7.30 (m, 3 H), 7.23-7.20 (m, 3 H), 7.16-7.10 (m, 4 H), 7.03-6.99 (m, 3 H), 6.87-6.85 (m, 3 H), 6.56-6.51 (m, 2 H), 6.40 (d, J = 7.8 Hz, 2 H), 5.82 (d, J = 9.2 Hz, 1 H), 5.04 (d, J = 9.0 Hz, 1 H), 3.73 (s, 3 H), 3.62 (s, 3 H); ¹³C NMR (100Hz, CDCl₃): δ 173.18, 146.26, 141.18, 139.44, 132.86, 129.28, 129.16, 129.03, 128.16, 127.47, 127.13, 121.41, 121.19, 119.44, 117.05, 113.10, 109.51, 62.00, 61.15, 52.20, 32.95; IR (neat): U 3411, 3025, 2954, 1718, 1603, 1507, 1469, 1365, 1252, 1157, 1089, 836, 800, 743, 698 cm^-1; dr (anti:syn) > 20:1; HRMS (ESI) Calcd for [C₃₁H₂₈N₂NaO₂, M + Na]⁺ : 483.2043; found: 483.2048; 97% ee (HPLC condition: Chiralcel OD-H column, n-Hexane/i-PrOH = 100:1, flow rate = 1.0 mL/min, wave length = 254nm, t_R = 10.45 min for minor isomer, t_R = 11.77 min for major isomer); [α]_D¹⁰ +74.9 (c 0.37, CH₂Cl₂).