HCID 86590267, compound → HCID 56980733, compound

Participants

Reaction Steps

Racemisation of benzyl 3-oxoethylidene-7-oxo4-oxa-1-azabicyclo[3.2.0] heptane-2-carboxylate (II):- A solution of the title compound (II) as a mixture of geometrical isomers E-Z (2:1) (162 mg, 0.56mmol) in chloroform (8 ml) was allowed to stand at ambient temperature away from strong light for three days. The solution was evaporated to dryness, chromatographed over silica gel in ethyl acetate-hexane (1:1), and, on evaporation, gave the title compound in the ratio of geometric isomers E-Z (1.7:1) (53 mg, 33%), [α]20+16.4° (c=2% in dichloromethane); addition of R-2,2,2-trifluoro-1-(9-anthryl)ethanol (1000% by weight) to the nmr solution (250 MHz, CDCl3) caused two sets of signals to appear for the 6b, 6a and 8 protons of both the E and Z isomers and for the 2 proton of the E isomer. Irradiation of specific protons demonstrated coupling between the 5 and 6 and the 8 and 9 protons for all these signals. The intensity of the signals indicated a 65:35 mixture of enantiomers. When the title compound was freshly prepared the geometric isomer ratio was E-Z (1.6:1), [α]20+53.9° (c=2% in dichloromethane); and addition of R-2,2,2 trifluro- 1-(9-antreyl)ethanol to the nmr solution showed a 93:7 mixture of enantiomers.

Provenance & Evidence