Synthetic studies on O-heterocycles via cycloadditions. Part 1. Photochemical (electron transfer sensitised) C-C cleavage of diaryloxiranes

Abstract

Irradiation of trans-stilbene oxide with naphthalene-1,4-dicarbonitrile as sensitiser in the presence of electron deficient dipolarophiles leads, via a presumed carbonyl ylide, to various dihydro- and tetrahydro-furans. This chemistry is extended, for the first time, to an example with both aryl rings oxygenated, 2,3-bis(p-methoxyphenyl)oxirane, using anthracene-9,10-dicarbonitrile as sensitiser; in contrast to stilbene oxide, in this case direct irradiation, triplet sensitisation, or thermal activation lead to C–O bond cleavage. The bis(p-methoxyphenyl) adducts, of interest in the lignan area, are formed with a lack of stereoselectivity suggestive of diradical intermediates.