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We have developed the Cp*Rh(III)-catalyzed cyclization reaction of arylnitrones with diazo compounds to obtain N-hydroxyindoline products under mild conditions. The substrate scope and functional group compatibility were examined with the demonstration of synthetic utility.

The first example of Rh(III)-catalyzed cyclization of arylnitrones to indolines under external oxidant-free conditions is presented. An intermolecular coupling of arylnitrones with internal alkynes is made possible by the dual role of the Cp*Rh(III) catalyst mediating both the C–H bond activation and O-atom transfer. Synthetically important and pharmacologically privileged indoline derivatives were obtained in good yields with high diastereoselectivity.

Catalytic 1,4-dioxo functionalizations of 3-en-1-ynes to (Z)- and (E)-2-en-1,4-dicarbonyl compounds are described. This regioselective difunctionalization was achieved in one-pot operation through initial alkyne hydration followed by in situ Selectfluor oxidation. The presence of pyridine alters the reaction chemoselectivity to give 4-hydroxy-2-en-1-carbonyl products instead. A cooperative action of pyridine and Zn(II) assists the hydrolysis of key oxonium intermediate.

The reaction proceeds as well with 3-en-1-ynamides who bear alternative withdrawing groups like tosyl instead of mesyl at the nitrogen.