Indium triflate-catalysed Diels–Alder reactions of isochromenylium cations with enones

Abstract

In the presence of indium triflate, o-alkynylbenzaldehydes form isochromenylium cations that react with enones such as chalcones and diarylidineacetones to give 1,2-dihydronaphthalenes in moderate to good yields. The reaction proceeds via a rare type of Diels–Alder reaction in which both the diene (isochromenylium cation) and the dienophile (enone) are electron deficient.