STUDIES OF A NOVEL BIOMIMETIC RADICAL SPIROCYCLISATION

The mechanism of the radical spirocyclisation 7 --> 9 has been investi gated, It has been shown by isotopic labelling that the biaryl ether o xygen 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 add ed water. The mechanism of Scheme I path a is proposed, involving oxyg en transfer from an aromatic nitro group to carbon in a cyclohexadieny l radical. Radical decarboxylation of the biarylamine derivative 29 do es not lead to spirodienone 9 but diverts instead to the azathiaacetal 30.