tert-butyl (1S)-1-formyl-2-methylpropyl(methyl)carbamate → Ethyl (2E,4S)-N-Boc-N-methyl-4-amino-2.5-dimethylhex-2-enoate

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Reaction Steps

To a solution of aldehyde 13 (1.75 g, 8.7 mmol) in dry CH2Cl2 (9.0 mL) under an argon atmosphere at room temperature was added (carbethoxyethylidene)triphenylphosphorane (4.19 g, 11.3 mmol) and stirring was continued for a 4 h. The reaction mixture was diluted with water (100 mL) and extracted with diethyl ether (3×100 mL). The combined organic extracts were washed with saturated aqueous sodium chloride (100 mL), dried with magnesium sulfate and concentrated in vacuo. The crude oil was purified by flash chromatography (silica gel, 2:23 diethyl ether-pet. ether) to afford the required E-2-alkenoate 14 as a colourless oil (2.13 g, 82% yield). 1H-NMR (200 MHz, CDCl3) 0.74 (d, J=6 Hz, 3H, CH3), 0.79 (d, J=6 Hz, 3H, CH3), 1.17 (t, J=0.7 Hz, 3H, CH3), 1.34 (s, 9H, Boc-(CH3)3), 1.72 (m, 1H, CH), 1.78 (s, 3H, —CH3), 2.60 (bs, 3H, NCH3), 4.08 (q, J=7 Hz, 2H, CH2), 4.15-4.20 (m, 0.5H, CH), 4.21-4.32 (m, 0.5H, CH), 6.54 (d, J=8 Hz, 1H, CH); Exact mass calc'd for C16H30N04 (M+H)+: 300.21750; Found (DCI): 300.21754. Optical rotation obtained was [α]D25 +61.1 (c 9.1, CHCl3).

Provenance & Evidence