The electrophilic cyanation of alkynyl halides (bromides or chlorides) with N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) using a zinc reagent

A novel Zn-mediated preparation of propiolonitriles using electrophilic cyanation of alkynyl bromides with N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) has been achieved here. The zinc dust was firstly used to activate the C(sp)–Br bond in the presence of tetrabutylammonium iodide (TBAI) to form an alkynyl zinc reagent in situ, which would undergo a nucleophilic addition with NCTS at the cyano group to afford an imine. Finally the propiolonitrile product was obtained after the elimination of the zinc complex. According to this new protocol, various phenylpropiolonitriles have been prepared from alkynyl bromides in moderate to excellent yields (51–95%), and could also be generated from the combination of inactive alkynyl chlorides with tetrabutylammonium bromide (TBAB) in lower yields (23–70%).