We report a Pd-catalyzed halocyclization of unactivated 1,6-diynes with N-bromosuccinimide(NBS).This approach produces stereo-defined dibromo substituted dihydropyrans,tetrahydropyridines,and 3-methylene cyclohexenes ...We report a Pd-catalyzed halocyclization of unactivated 1,6-diynes with N-bromosuccinimide(NBS).This approach produces stereo-defined dibromo substituted dihydropyrans,tetrahydropyridines,and 3-methylene cyclohexenes with exocyclic double bond appendages in mostly good yields.Copper salt was found to be a useful Lewis acid in this reaction.Mechanistically,a formal anti-carbopalladation and a bromide radical promoted PdⅡ-PdⅢ-PdⅠ-PdⅡcatalytic cycles were proposed to be involved in the formation of the dibromo-substituted products.Further functionalization of the dihydropyran derivatives underwent B(C6F5)3-catalyzed ring opening,and reduction afforded dibrominated 1,3-dienes with excellent stereoselectivity.展开更多
基金National Natural Science Foundation of China(No.21961015)the Natural Science Foundation of Jiangxi Province(No.20202ACBL203005)for financial supportthe Open Project Program of Polymer Engineering Research Center,Jiangxi Science&Technology Normal University(No.KFGJ18014)。
文摘We report a Pd-catalyzed halocyclization of unactivated 1,6-diynes with N-bromosuccinimide(NBS).This approach produces stereo-defined dibromo substituted dihydropyrans,tetrahydropyridines,and 3-methylene cyclohexenes with exocyclic double bond appendages in mostly good yields.Copper salt was found to be a useful Lewis acid in this reaction.Mechanistically,a formal anti-carbopalladation and a bromide radical promoted PdⅡ-PdⅢ-PdⅠ-PdⅡcatalytic cycles were proposed to be involved in the formation of the dibromo-substituted products.Further functionalization of the dihydropyran derivatives underwent B(C6F5)3-catalyzed ring opening,and reduction afforded dibrominated 1,3-dienes with excellent stereoselectivity.
