Reaction Steps
Preparation of 3-oxoethylidene-7-oxo-4-oxa-1-azabicyclo [3.2.0] heptane (V) from synthetic (I):- A solution of (D) (21.6 mg, 11 mol) prepared by hydrogenation of benzyl 3-oxoethylidene-7-oxo-4-oxa-1-azabicyclo[3.2.0]heptane-2-carboxylate (II) (90 mg, 0.31 mmol) in tetrahydrofuran (90 ml) was allowed to stand at room temperature for four hours when h.p.l.c. (conditions B) showed no further increase in the signal due to (E-V). The reaction mixture was evaporated to dryness and redissolved in ethyl acetate (50 ml). The ethyl acetate solution was washed with saturated NaHCO3, 0.1M HCl and saturated NaCl, dried with magnesium sulphate, and evaporated to an oil (50 mg). Semi-preparative h.p.l.c. of this residue (conditions C) gave E-3-oxoethylidene-7-oxo-4-oxa- 1 -azabicyclo[3.2.0]heptane (8.3 mg, 49%) CD Δε237.4 6.1 CH3CN); λmax.(CH3CN) 249 nm (εl3,399 dm3 mol−1 cm−1); Vmax. 1 794, 1 669, 1 638, and 1 591 cm−1;, δH(250 MHz, CDCl3) 3.19 (1H, d, J 16.7 Hz, 6β-H), 3.59 (1H, ddd, J 0.9, 2.8 and 16.6 Hz, 6α-H), 3.99 (1H, d, J 17.5 Hz, 2α-H), 5.06 (1H, dd, J 1.5 and 17.4 Hz 2β-H), 5.72 (1H, d, J 2.8 Hz, 5-H), 5.87 (1H, ddd, J 1.7, 1.7 and 3.5 Hz, 8-H) and 9.57 (1H, d, J 5.0 Hz, 9-H); addition of R-2,2,2-trifiuoro-1-(9-anthryl)ethanol (1000%) caused separation of the signals due to the 2β proton chemical shift caused both sets of 2β protons to loose their smaller coupling. The two sets of 2β proton signals were in the ratio 2:1 m/z 153 (M+, 23%), 125 (M+-CO, 12%), 111 (M+CH2CO, 24%) and 55 (M+-98, 100%). Further elution gave Z-3-oxoethylidene-7-oxo-4-oxa-1-azabicyclo[3.2.0]heptane containing 5% of the E isomer (2.3 mg, 14%), Vmax. 1 792 and 1 660 c−1 (br); dH (250 MHz, CDCl3) 3.25 (1H, d, J 16.8, 6b-H), 3.52 (1H, ddd, J 0.8, 2.8 and 16.9 Hz, 6α-H), 3.85 (1H, d, J 16.8 Hz, 2α-H), 4.68 (1H, dd, J 0.8 and 17.0 Hz, 2β-H), 5.23 (1H, dt, J 1.0 and 7.9 Hz, 8-H), and 9.96 (1H, d, J 7.8 Hz); m/z 153 (M+24%) 125 (M+CO, 11%) 111, (M+CH2CO, 29%), and 55 (M+-98, 100%).
