FORMATION OF TRANS RING-FUSED COMPOUNDS BY AN ALKYLATION-RADICAL CYCLIZATION SEQUENCE

Enolates derived from bicyclic lactones of type 1 (Scheme I) can be alkylated with 2-propynylic halides to give products 2, in which the unsaturated alkyl group is syn to the adjacent ring-fusion hydrogen. Reaction of 2 with sodium phenyl selenide and then with diazomethane produces esters 3, and these give trans ring-fused bicyclic compounds 4 when treated with triphenyltin hydride in the presence of a radical initiator. The bicyclic compounds afford ketones on double-bond cleavage, and the angular ester function can be converted into a methyl group. Similar processes occur if an aldehyde is used in the first step instead of a halide. The methodology is general.