反应详情

A solution of 4-allyl-3-benzyl-1-(1-benzyloxycarbonyl-1-triphenylphosphoranylidenemethyl)azetidine-2-one (36) (0.38 g) in ethyl acetate (20 ml) was treated with trifluoroacetic acid (1.0 ml). The solution was cooled to -78° and ozone passed through it until it just became blue in colour. The excess ozone was blown off in a stream of argon and a solution of triphenylphosphine (0.16 g) in ethyl acetate (2 ml) was then added. The reaction solution was purged with argon for the next 30 minutes and the reaction flask was then transferred to an ice bath. Saturated aqueous sodium bicarbonate (30 ml) was added with vigorous stirring and after a further 30 minutes the ethyl acetate solution was separated, washed with brine and dried over sodium sulphate. Column chromatography on silica gel 60 (<230 mesh) eluting with ethyl acetate/60°-80° petroleum ether 3:7 gave benzyl 6-benzyl-7-oxo-1-azabicyclo[3,2,0]hept-2-ene-2-carboxylate as the trans isomer (37) (0.09 g. 42%). It was a colourless gum; νmax (CHCl3) 3020, 2960, 1785, 1725 and 1610 cm-1 ; τ (CDCl3) 2.6-3.0 (10H, m, phenyls), 3.66 (1H, t, J 3 Hz, C3-H), 4.80 (2H, s, benzyl CH2 -O), 6.02 (1H, td, J 81/2 and 3 Hz, C5-H), 6.60 (1H, ddd, J 9, 6 and 3 Hz, C6-H), 6.88 (1H, d, J 6 Hz, inner signal of ABX for PhCH2 -C6), 6.97 (1H, d, J 9 Hz, inner signal of ABX for PhCH2 -C6), 7.29 and 7.32 (2H, each a dd, J 81/2 and 3 Hz, inner signals of AB for C4-H2).

1. temperatureThe solution was cooled to -78°
2. customThe reaction solution was purged with argon for the next 30 minutes
3. customthe reaction flask was then transferred to an ice bath
4. additionSaturated aqueous sodium bicarbonate (30 ml) was added
5. customwas separated
6. washwashed with brine
7. dry with materialdried over sodium sulphate
8. washColumn chromatography on silica gel 60 (<230 mesh) eluting with ethyl acetate/60°-80° petroleum ether 3:7