Rhodium-Catalyzed Cycloisomerization of 1,6-Enynes with an Intramolecular Halogen Shift
铑催化的1,6-烯炔环异构化反应研究（英文）

A Rhodium (Ⅰ)-species catalyzed cycloisomerization reaction of a wide spectrum of 1,6- enynes with an unusual intramolecular halogen shift was investigated. This Rh-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined α-halomethylene-γ-butyrolactones,lactams, tetrahydrofurans, pyrrolidines and cyclopentanes. Coordinatively unsaturated rhodium species ( Rh(COD)Cl]2 + dppb + AgSbF6 ) only catalyzes the reaction with enyne substrates bearing a Z-form double bond. Neutral rhodium species (RhCl(PPh3)3 ) can catalyze enyne substrates bearing a Z- or E-form double bond to form the desired products and has a wider substrate scope. The mechanism of the reaction was studied by the employment of control experiments with different enyne isomers and a π-allyl rhodium intermediate was suggested to explain the formation of the cyclic products with an intramolecular halogen shift. Further transformation of the halo-alkenyl species can be readily achieved through metalcatalyzed Suzuki cross-coupling reactions.