1,3-Dipolar cycloaddition of 2- and 3-nitroindoles with azomethine ylides. A new approach to pyrrolo[3,4-b]indoles

The 1,3-dipolar cycloaddition of unstabilized azomethine ylides with 2- and 3-nitroindoles furnishes the expected hexahydropyrrolo[3,4-b]indole cycloadducts in good to excellent yields. The cycloadducts can be denitrated with Bu3SnH/AIBN, and cycloadduct 5 was oxidized with MnO2 to yield the known pyrrolo[3,4-b]indole 13.