Attempts at vinyl radical carbonylation through cyclization onto carbonyl and cyano groups

Sulfanylvinyl radicals 4-6, 16, produced From toluenesulfanyl radical addition to alkynes 1-3, 15, gave only products arising from cyclization onto the thiophenyl ring and H-abstraction. No products were obtained deriving from possible 5-membered cyclization onto the esteric or thioesteric carbonyl group. Similar results were obtained from toluenesulfanyl radical addition to alkynyl nitriles 20 and 24, which did not provided any evidence for 5- or 6-membered vinyl radical cyclization onto the aliphatic cyano group, In contrast, both toluenesulfanyl- and benzenesulfanyl- vinyl radicals 32 and 37a smoothly cyclize onto the aromatic cyano group leading to ketones 35 and 39. This protocol represents a novel indirect radical carbonylation and provides a useful synthetic approach to indenones, (C).