Development of new radical reactions - Skeletal rearrangement via alkoxy radical and asymmetric radical cyclization in the presence of Lewis acid

Two new radical reactions are reviewed. 1) Skeletal rearrangement via alkoxy radical;a new radical rearrangement, initiated by radical cyclization between ketones and acetylenes followed by beta-cleavage of the alkoxy radical and subsequent radical-olefin cyclization was developed. This reaction realized a single-step conversion from cyclohexanone derivatives to bicyclic cyclooctenones and from cyclopentane derivatives to bicyclic cycloheptenenones. The efficiency of the conversion was greatly influenced by the substituents on the ring and on the side chain. Same type of rearrangement was also observed in the radical reaction of epoxydecalin thiocarbonylimidazolides prepared from 1-hydroxymethyl-1, 2, 3, 4, 4a, 5, 6, 7, 8-octahydronaphthalene derivatives. 2) Asymmetric radical cyclization in the presence of Lewis acid : beta-diastereoselective radical cyclizations using alpha,beta-unsaturated 8-phenylmenthyl ester as a chiral radical acceptor was developed. Generally, higher diastereoselectivity was observed when bulky Lewis acid was used at low temperature. Go-ordination of the Lewis acid to the carbonyl oxygen fixed the conformation of alpha,beta-unsaturated ester as s-trans and activated the unsaturated ester as a radical acceptor, chiral (2-methylenecyclopentyl) acetate, (2-methylenecyclohexyl) acetate, (2-cyclopentnly) acetate, and (2-cyclohexenyl) acetate were prepared.