Vinylcyclopropylacyl and polyeneacyl radicals. Intramolecular ketenealkyl radical additions in ring synthesis

Abstract

Treatment of a variety of substituted vinylcyclopropyl selenyl esters, e.g.11, with Bu₃SnH–AIBN in refluxing benzene leads to the corresponding acyl radical intermediates, which undergo rearrangement and intramolecular cyclisations via their ketene alkyl radical equivalents producing cyclohexenones in 50–60% yield. By contrast, treatment of conjugated triene selenyl esters, e.g.32, with Bu₃SnH–AIBN produces substituted 2-cyclopentenones via intramolecular cyclisations of their ketene alkyl radical intermediates. Under the same radical-initiating conditions the selenyl esters derived from o-vinylbenzoic acid and o-vinylcinnamic acid undergo intramolecular cyclisations producing 1-indanone and 5,6-dihydrobenzocyclohepten-7-one respectively in 60–70% yields. A tandem radical cyclisation from the α,β,γ,δ-diene selenyl ester 31 provides an expeditious synthesis of the diquinane 35 in 69% yield.