Ring Opening Reaction of Epoxides under Aryl Acetylene/ZnBr2/DIEA Conditions

Abstract

Recently, we have reported the usefulness of ZnBr2/DIEA (N,N-diisopropylethylamine) combination for the in situ generation of zinc acetylide species from terminal acetylenic compounds. We applied the system to the reactions with Ntosylimines, activated quinolinium salts, and carboxylic acid chlorides. The alkynylation of epoxide via ring opening with metal acetylide is an important carbon-carbon bond forming reaction. However, this useful reaction suffers from some intrinsic limitations including low yields and regioselectivity. Recently, several new methods have been suggested in order to solve these problems. Lithium acetylide in the presence of BF3 etherate 3a or Et2AlCl, 3b,3c titanium acetylides, trimethylgallium-catalyzed lithium acetylide in the presence of LiClO4 3f all afford better yields than the classical methods. The ring opening reaction of epoxide with these reagent combinations proceeded at the least hindered position without a special substituent which control the approach of the metal acetylide by chelation with the special substituent. Recently, regioselective ring opening of epoxide with lithium alkynyl trimethylaluminium ate complex in the presence of BF3 etherate was reported. 4c In these respects, we decided to examine the feasibility of the alkynylation of epoxide with ZnBr2/DIEA system. 1