Nickel-iminophosphine-catalyzed [4 + 2] cycloaddition of enones with allenes: synthesis of highly substituted dihydropyransf

摘要

Enones were found to react with allenes intermolecularly in the presence of a catalytic amount of a nickel-iminophosphine complex to provide dihydropyrans via oxidative cyclization of an enone and Ni(0). The hetero Diels-Alder reactions of α,β-unsaturated carbonyl compounds with carbon-carbon double bonds are a useful method for the synthesis of dihydropyrans, which are privileged structural subunits in numerous important natural products and in Pharmaceuticals.1,2 Although there are a large number of examples for syntheses of dihydropyrans by hetero Diels-Alder reactions, the use of an enol ether as an electron-rich hetero-dienophile is mandatory for sufficient transformation, and an