反应详情

A solution of 4allyl-3-methyl-1-(1-benzyloxycarbonyl-1-triphenylphosphoranylidenemethyl)azetidine-2-one (38) (0.29 g) in ethyl acetate (25 ml) was treated with trifluoroacetic acid (0.4 ml) and then cooled to -78°. Ozone was bubbled through the solution until it just became pale blue in colour. The excess ozone was blown off in a stream of argon and an ethyl acetate solution of triphenylphosphine (0.14 g) was then added. After a further 10 minutes the reaction flask was transferred to an ice bath and saturated aqueous sodium bicarbonate (45 ml) was added with vigorous stirring. This was continued for 30 minutes and the ethyl acetate solution was then separated, washed with brine and dried over sodium sulphate. The solution was concentrated and chromatographed on silica gel 60 (<230 mesh) eluting with ethyl acetate/60°-80° petroleum ether mixtures grading from 3:7 to 6:4. This gave the trans-isomer of benzyl 6-methyl-7-oxo-1-azabicyclo[3,2,0]hept-2-ene- 2-carboxylate (39) (0.08 g, 55%); νmax (CHCl3) 3000, 1780, 1725 and 1615 cm-1 ; δppm ((CD3)2CO) 1.34 (3H, d, J 7 Hz, CH3), 2.85 (2H, dd, J 9 and 2 Hz, C4-H2), 3.24 (1H, dq, J 3 and 7 Hz, C6-H), 3.91 (1H, dt, J 3 and 9 Hz, C5-H), 5.20 (2H, s, benzyl CH2), 6.45 (1H, t, J 2 Hz, C3-H) and 7.2-7.5 (5H, m, phenyl); (M+ at m/e 257.1052 C15H15NO3 requires 257.1051).

1. temperaturecooled to -78°
2. customOzone was bubbled through the solution until it just became pale blue in colour
3. additionan ethyl acetate solution of triphenylphosphine (0.14 g) was then added
4. additionsaturated aqueous sodium bicarbonate (45 ml) was added with vigorous stirring
5. waitThis was continued for 30 minutes
6. customthe ethyl acetate solution was then separated
7. washwashed with brine
8. dry with materialdried over sodium sulphate
9. concentrationThe solution was concentrated
10. customchromatographed on silica gel 60 (<230 mesh)
11. washeluting with ethyl acetate/60°-80° petroleum ether