Regioselectivity of the Singlet Oxygen Ene Reaction (Schenck Reaction) with Vinylsilanes

Article abstract of DOI:10.1021/jo00091a020

The ene reaction of singlet oxygen and vinylsilanes 1 with various substitution patterns and double-bond geometry has been studied. β-Silyl allylic hydroperoxides 2 were the major products of the photooxygenation, accompanied by smaller amounts of α,β-unsaturated ketones 3.The latter derive from decomposition of the regioisomeric α-hydroperoxy silanes 4 by elimination of silanol.Regioselectivities up to 97:3 were observed for vinylsilanes with a methyl group geminal to the silyl group and with cyclic derivatives.Z-Configurated substrates showed lower regioselectivity and reactivity.Elongation of the carbon chain at the geminal position also increased the amount enone formed.These results are rationalized in terms of stereoelectronic effects imposed by the silyl group on the ring-opening of the perepoxide intermediate.