Tetrahydrofuran → (2S,3S,alphaS)-t-Butyl 3-(N-allyl-alpha-methylbenzylamino)-2-hydroxy-3-phenylpropionate

Participants

Reaction Conditions

Reaction Steps

A solution of (S)-N-allyl-α-methylbenzylamine (2) (1.94 g, 12.1 mmol) in anhydrous tetrahydrofuran (25 ml) was cooled to -78° C. and 1.6M butyllithium (6.03 ml, 9.6 mmol) was added dropwise via a syringe. The resulting orange lithium amide solution was stirred at -78° C. for 1 hour. A solution of t-butyl cinnamate (7) (1.64 g, 8.1 mmol) in anhydrous tetrahydrofuran (15 ml) was then added via a cannula and the solution was stirred for a further 1 hour. The resulting yellow enolate solution was then diluted with anhydrous tetrahydrofuran (30 ml) and solid (+)-(camphorsulphonyl)-oxaziridine (2.76 g, 12.1 mmol) was added. After stirring for a further 6 hours at -78° C., the mixture was warmed to 0° C. (15 minutes) and quenched by the addition of saturated aqueous ammonium chloride solution. Ethyl acetate (50 ml) was added, followed by brine (10 ml). The organic layer was separated, dried (magnesium sulphate) and filtered and the solvent was evaporated under reduced pressure to afford an oily solid residue. Treatment of this with diethyl ether precipitated the oxaziridine/sulfonimine which was removed by filtration and the resulting oil was purified by flash chromatography on silica gel [ethyl acetate/petroleum ether (1:19)] affording the title compound (Rf 0.20) as a colourless oil (2.89 g, 95%). δH (300 MHz: CDCl3) 7.50-7.21 (10H, m, Ph), 5.89 (1H, m, NCH2CH=CH2), 5.12 (1H, app. dd, J=17.2 and 41.4, trans CH=CH2), 5.04 (1H, app. dd, J=17.2 and 1.4, cis CH=CH2), 4.53 (1H, d, J=3.8, CHOH), 4.23 (1H, d, J=3.8, NCHCH), 4.13 (1H, q, J=6.8, PhCHCH3), 3.47 (1H, app. dd, J=15.6 and 7.1, NCH2), 3.03 (1H, bs, OH), 1.29 (9H, s, (CH3)3CH), 1.21 (3H, d, J=6.8, PhCHCH3).

Provenance & Evidence