Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

Abstract

Abstract The versatility of the trityl cation (TrBF 4 ) as a highly efficient Lewis acid organocatalyst is demonstrated in the oxa‐Diels–Alder reaction of various unactivated aromatic and aliphatic aldehydes and simple unactivated dienes, such as isoprene and 2,3‐dimethylbutadiene. The transformation proceeds smoothly to give 3,6‐dihydropyrane adducts in high to moderate yields with catalyst loadings down to 1.0 mol‐% under mild reaction conditions. In contrast to most previously reported strategies, this protocol does not require substrate functional group activation, neither by electron‐deficient aldehydes (2‐oxo aldehydes) or electron‐rich dienes (methoxy or amino‐butadiene).