Substituent effect of imino-o-arenesulfonates, a coupling partner in Suzuki-Miyaura reaction for substitution of the pyrazine ring: A study for the synthesis of coelenterazine analogs

Article abstract of DOI:10.1246/bcsj.82.870

Amino(aryl)pyrazines, a key intermediate in the synthesis of coelenterazine and its analogs, can be prepared in excellent yields by utilizing imino-O-tosylates in the SuzukiMiyaura reaction. These imino-O-tosylates serve as a substitute for the corresponding imino-O-triflates, which are sometimes too unstable to be stored during the optimization of the reaction conditions. Aryltrifluoroborates, a coupling partner, worked well when arylboronic acids or arylboronate esters were less reactive. Aryltrifluoroborates also worked well when containing an electron-donating group attached to the aromatic ring. The study of the substituent effect of imino-O-arenesulfonates demonstrated a major difference in the rate of the reactions when changing from electron-donating groups to electron-withdrawing groups at the para position of arenesulfonates. Imino-O-arenesulfonate containing a para-bromo substituent only gave the desired coupling product leaving the para substituent of arenesulfonate untouched.