Photooxygenation of vinylstannanes: tin-substituted allylic hydroperoxides through the regio- and diastereoselective ene reaction with singlet oxygen

Abstract

For the first time the photooxygenation of vinylstannanes 1 was investigated. Thus, dye-sensitized oxygenation of acylic and cyclic tri- and tetrasubstituted vinylstannanes yielded regioselectively β-stannylallylic hydroperoxides 2 in all cases. As byproducts were formed the α,β-enones 3', which derive from the regioisomeric ene product 3 through elimination of trialkyltin hydroxide. The degree of regioselectivity depended on the configuration of the precursor olefin as well as on the substitution pattern at the tin atom. Comparison with the analogous olefinic carbon and silicon compound reveals that the high degree of gem selectivity in the ene reaction of vinylstannanes is the result of composite steric and electronic factors reflected in the perepoxide intermediate