Indium(iii) triflate-catalysed [4 + 2] benzannulation reactions of o-alkynylbenzaldehydes with enolisable carbonyl compounds: selective synthesis of naphthyl ketones

Abstract

Indium(III) triflate is found to be an effective catalyst for the benzannulation reactions of o-alkynylbenzaldehydes with enolisable aldehydes, ketones, 1,3-diketones and β-keto esters. The reactions produce naphthyl ketones through ring opening of adducts arising from the inverse electron demand Diels–Alder reactions between in situ generated isochromenylium cations and enols. The main feature of the method is selective formation of naphthyl ketones in a highly regioselective manner without any decarbonylation.