Stereoselectivity in the intramolecular cycloaddition of double bonds to triplet benzenes

Abstract

The diastereoselectivty with which o- and p-butenoxy acetophenones undergo intramolecular 2 + 2 photocycloadditions has been measured in several respects. The five- and four-membered rings of the tricyclo[6.3.O.O]undecadiene photoproducts are always anti to each other and all-cis with respect to the six-membered ring. This fact indicates that the photoinduced electrocyclization to a cyclobutene of one diene unit of the bicyclo[6.3.O]undecatriene intermediate puckers in only one of two possible ways. Alkyl groups originally on the tether or the double bond show high diastereoselectivity with regard to the bridgehead stereocenters.