Regioselective Synthesis of Indolopyrazines through a Sequential Rhodium-Catalyzed Formal [3+3] Cycloaddition and Aromatization Reaction of Diazoindolinimines with Azirines

A regioselective
synthetic method for the preparation of indolopyrazines
was demonstrated through a sequential Rh-catalyzed formal [3+3] cycloaddition
and aromatization reaction of a wide range of diazoindolinimines with
azirines. Because the previously reported synthetic methods afforded
mixtures of indolopyrazines, the present method using unsymmetrical
azirines has a strong advantage from a regioselectivity viewpoint.