alpha-ketene alkyl and alpha,beta-unsaturated acyl radical intermediates in ring constructions

Treatment of the E-alpha,beta-unsaturated selenyl esters 1 and 3a with Bu(2)SnH-AIBN produces the corresponding cyclohexenones 2 and 7/8 respectively via presumed alpha-ketene alkyl radical intermediates. In a similar manner the cyclopropyl ester 9 leads to a mixture of 12 and 13, and the 2,7-diene selenyl ester 15 undergoes a novel bi-cyclisation producing the diquinane 17 in 76% yield.