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.
Ruvinskaya, J. O., Rostovskii, N. V., Filippov, I. P., Khlebnikov, A. F., & Novikov, M. S. (2017). 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. Organic and Biomolecular Chemistry, 16(1), 38–42. https://doi.org/10.1039/c7ob02637d