A novel approach to 5: H -pyrazino[2,3- b] indoles via annulation of 3-diazoindolin-2-imines with 2 H -azirines or 5-alkoxyisoxazoles under Rh(II) catalysis

Abstract

A novel one-step method for the preparation of 5H-pyrazino[2,3-b]indoles with different substitution patterns in all rings of the tricyclic system via the Rh2(OAc)4-catalyzed reaction of 2H-azirines with 3-diazoindolin-2-imines is reported. Alkyl 5H-pyrazino[2,3-b]indole-3-carboxylates were also prepared by a one-pot procedure from synthetic equivalents of alkyl 2H-azirine-2-carboxylates, 5-alkoxyisoxazoles. The reactions provide the first examples of the use of Rh(ii) catalysis for intermolecular annulations with 2H-azirines and isoxazoles.