Photocatalytic Synthesis of Indanone, Pyrone, and Pyridinone Derivatives with Diazo Compounds as Radical Precursors.

We disclose herein a photocatalytic radical cascade cyclization of diazoalkanes for the divergent synthesis of important carbocycles and heterocycles. Under the optimal reaction conditions, various indanone, pyrone, and pyridinone derivatives can be obtained in moderate to good yields. Mechanistic experiments support the formation of carbon-centered radicals from diazoalkanes through the proton-coupled electron transfer process. Scale-up reaction using continuous flow technology and useful downstream application of the formed heterocycles further render the strategy attractive and valuable.

Photochemical synthesis of 1,2,4-triazoles via addition reaction of triplet intermediates to diazoalkanes and azomethine ylide intermediates.

The reactivity of diazoalkanes most commonly proceeds through the formation of carbene intermediates or dipolar cycloaddition reactions. The reaction of diazoalkanes with intermediates with unpaired electrons, however, is much less elaborated. Herein, we report on the photochemical reaction of acceptor-only diazoalkanes with azodicarboxylates. Photoexcitation of the latter results in the formation of a triplet species, which undergoes an addition reaction with diazoalkanes and formation of an azomethine ylide followed by dipolar cycloaddition reaction with organic nitriles to give a 1,2,4-triazole. The application of this transformation was elaborated in a broad and general substrate scope (48 examples), including scale-up via flow chemistry and downstream transformations. Experimental and computational studies were performed to elucidate the reaction mechanism and to rationalize the reaction outcome.