MPHT-Promoted bromocyclization of of ortho-substituted arylalkynes: Application to the synthesis of 2-substituted 3-bromobenzofurans and -benzo[b]thiophenes
A convenient: and general approach to the synthesis of 2substituted 3-bromobenzofurans and -benzothiophenes was developed. The procedure is based, on the cyclization of orfho-substituted arylalkynes in the presence of N-methylpyrrolidin-2-one hydrotribromide (MPHT) as a soft and easy-tohandle electrophilic brominating reagent. Under mild reaction conditions, MPHT promoted the bromocyclization of various enynes and diynes as well as arylalkynes to give 2substituted 3-bromobenzofurans and -benzothiophenes in. high to excellent: yields. Subsequent: functionalization by palladium-catalyzed coupling reactions at the C-Br bond afforded general access to 2,3-disubstituted benzofurans and benzothiophenes of biological interest.