On the understanding of BF3·Et2O-promoted intra- and intermolecular amination and oxygenation of unfunctionalized olefins

Abstract

BF₃·Et₂O was found to be effective for both intra- and intermolecular amination and oxygenation of unfunctionalized olefins. In the presence of 3 equiv. of BF₃·Et₂O, intramolecular hydroamination of N-(pent-4-enyl)-p-toluenesulfonamides, N-(hex-5-enyl)-p-toluenesulfonamides, intermolecular hydroamination between sulfonamides and cyclohexene, norbornene or styrene, lactonization of pent-4-enoic acid or hex-5-enoic acid compounds and esterification of cyclohexene with different carboxylic acids all proceeded readily, leading to the corresponding amination or oxygenation products in up to 99% isolated yields. Preliminary NMR experiments and DFT calculations suggested that the intramolecular hydroamination reactions proceeded via a sulfonimidic acid intermediate (NS–OH), and formation of the corresponding Brønsted acid HF or HBF₄ was less likely.