Studies of a novel biomimetic radical spirocyclisation

Abstract

The mechanism of the radical spirocyclisation 7→9 has been investigated. It has been shown by isotopic labelling that the biaryl ether oxygen does not emerge as the carbonyl group oxygen in the product, nor does the latter arise by hydrolysis of an intermediate e.g. 33 by added water. The mechanism of Scheme 1 path a is proposed, involving oxygen transfer from an aromatic nitro group to carbon in a cyclohexadienyl radical. Radical decarboxylation of the biarylamine derivative 29 does not lead to spirodienone 9 but diverts instead to the azathiaacetal 30.