新規ラジカル反応の開発-アルコキシラジカルを経る骨格変換反応およびルイス酸存在下における不斉ラジカル環化反応-

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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 β-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 : β-diastereoselective radical cyclizations using α, β-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. Co-ordination of the Lewis acid to the carbonyl oxygen fixed the conformation of α, β-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.
社団法人有機合成化学協会の論文
1996-01-01