Catalysed Diels–Alder reactions. The realization of orientation control with a bifunctional aliphatic dienophile

Abstract

The Lewis acid catalysed addition of methyl trans-4-oxobutenoate (7) to trans-piperylene (8) gives selectively product 9. SnCl₄ is a particularly efficient catalyst. A postulate of the preferential formation of a complex with the formyl group is used to explain the regio- and stereo-specificity of the reaction. Synthetic implications of this finding are discussed.