Photochemical multicomponent transformation of acceptor-only diazoalkanes by merging their cycloaddition and carbene reactivities

Herein, we report an efficient photochemical method for the synthesis of poly-substituted pyrazoles through a multicomponent reaction of acceptor-only diazoalkanes, alkynes, and solvents (cyclic ethers or nitriles). The key to this success was driven by the photolysis of acceptor-only diazoalkanes to form free carbene species and the fast in situ [3 + 2]-cycloaddition formation of nucleophilic NH pyrazole derivatives. This work also serves as an entry to allow future reaction design on the combination of carbene reactivity of diazoalkanes with their other reaction modes.