Facile regio- and stereo-chemical control in epoxy-allylic stannane cyclisations

Abstract

Lewis acid and butyllithium promoted cyclisations of epoxy-allylic stannanes have been studied. The regio-and stereo-chemistry of the cyclisations are described. The stereoelectronically favoured 5and 6-membered ring formations have been explained by either the electronic nature of, or the steric hindrance induced by, the epoxide moiety of the substrates depending on whether the reaction was promoted by a Lewis acid or butyllithium, respectively. The different stereoselectivities observed are brought about by the mode of reaction. The contrasting results for the 5-membered ring formations are particularly remarkable.