Palldium-Catalyzed Synthesis Of Cis-1,2-dihaloalkenes

cis-1,2-Dihaloalkenes are important building blocks in organic chemistry. However, there are only limited methods for the regio-and setereoselective synthesis of ci-1,2-dihaloalkenes. By trapping the intermediate resulting from the halopalladation of haloalkynes with different electrophiles, some effective approaches to cis-1,2-dihaloalkenes have been developed herein. The whole work consists of three parts:Firstly, an efficient and practical method for the synthesis of cis-1,2-dihaloalkenes has been realized by Pd-catalyzed coupling of alkynyl halides with α,β-unsaturated carbonyls under mild reaction conditions. It represents the first regio-and stereoselective halopalladation process of haloalkynes.Then, a Pd-catalyzed dienylation of alkynyl halides using2,3-butadienyl acetates is found to provide (1Z)-1,2-dihalo-3-vinyl-1,3-dienes in good yields and excellent stereoselectivity. It is worth to mention that2,3-butadienyl acetate, an allene, is used to capture the halopalladation intermediate for the first time.Finally, an unprecedented Pd-catalyzed hydrohalogenation of alkynyl halides for the regio-and stereoselective synthesis of (Z)-1,2-dihaloalkenes has been achieved employing [(allyl)PdCl]2as the catalyst and cis,cis-1,5-cyclooctadiene as the ligand. The advantages of this protocol are well illustrated by the assembly of trisubstituted (Z)-alkenes from1-bromo-2-chloroalkenes via iterative cross-coupling reactions. Notably, it represents one of the rare exmaples undergoing the protonation of alkenyl C-Pd bond.