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

摘要

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