Access to tetrahydrophenanthridine N-oxides via Rh(III)-catalyzed cascade C–H activation/cyclization of cyclic 2-diazo-1,3-diones and aryloximes

An efficient and straightforward protocol for the synthesis of tetrahydrophenanthridine N-oxides has been achieved from easily available cyclic 2-diazo-1,3-diones with aryloximes. This transformation proceeded through Rh(III)-catalyzed C–H activation and subsequent intramolecular cyclization under mild conditions, and involved the formation of two new bonds (C–C & C–N) in a single reaction vessel for the construction of novel fused isoquinoline N-oxides, with N2 and H2O being generated as the only by-products. Noteworthy, the process could be easily performed in one mmol scale as well as scaled up to gram-scale synthesis without reducing the percentage yield.