Chemistry of oxa- and aza-bicyclic(4.1.0)heptenes, total synthesis of (+)-pancratistatin

Vinyloxiranes 6a-b and vinylaziridines 7a-b were prepared efficiently from halocyclohexadiene-cis-diols 1. Reactions of 6 and 7 with a variety of organometallic reagents were investigated in order to determine the stereo- and regiochemistry of ring opening with carbon nucleophiles. The results indicate that 6 and 7 could serve as useful new synthons for C-disaccharides and Amaryllidaceae alkaloid syntheses.

The utility of synthon 7b has been demonstrated by a concise enantiocontrolled synthesis of (+)-pancratistatin (9). The key step involved the S_N2 opening of 7b with the aryl cyanocuprate derived from amide 217 to generate the pivotal cyclization precursor.