General and efficient synthesis of 1,2-dihydropyrrolo[3,4-b]indol-3-ones via a formal [3 + 2] cycloaddition initiated by C–H activation

Abstract

A [Cp*RhCl₂]₂-catalyzed formal [3 + 2] cycloaddition between isocyanates and indoles with electron-deficient alkenes at the C3-position of the indole moiety and directing groups at the N1-position of the indole moiety has been described. Undergoing sequential coupling reaction initiated by C–H activation and aza-Michael addition, a series of 1,2-dihydropyrrolo[3,4-b]indol-3-ones were successfully afforded in moderate to good yields by the formation of one C–C bond and one C–N bond. Interestingly, the pyridyl group at the N1-position of the indole moiety not only plays a role as the directing group, but also catalyses further intramolecular Michael addition as a base.