C-H Activation-Based Traceless Synthesis via Electrophilic Removal of a Directing Group. Rhodium(III)-Catalyzed Entry into Indoles from N-Nitroso and α-Diazo-β-keto Compounds.

A distinct C-H activation-based traceless synthetic protocol via electrophilic removal of a directing group is reported, complementing the currently exclusively used nucleophilic strategy. Rh(III)-catalyzed, N-nitroso-directed C-H activation allows the development of a traceless, atom- and step-economic, cascade approach for the synthesis of indole skeletons, starting from readily available N-nitroso and α-diazo-β-keto compounds. Importantly, the cyclization/denitrosation reaction represents a hitherto unobserved reactivity pattern for the N-nitroso group.