N-heterocyclic carbene catalyzed [4+2] cycloaddition of nitroalkenes with oxodienes

NHC catalysis: N-heterocyclic carbenes were found to be efficient catalysts for the unprecedented [4+2] cycloaddition of nitroalkenes and oxodienes, giving the corresponding dihydropyrans in good yield with good diastereoselectivity (see scheme). Deuteration experiment reveals that the reaction is possibly initiated by the addition of N-heterocylic carbene to nitroalkenes.