Multisubstituted pyrazole synthesis via [3 + 2] cycloaddition/rearrangement/N[sbnd]H insertion cascade reaction of α-diazoesters and ynones

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The cascade reactions of alkyl α-diazoesters and ynones using Al(OTf)3 as the catalyst are described. A series of 4-substituted pyrazoles were obtained via [3 + 2] cycloaddition, 1,5-ester shift, 1,3-H shift, and NH insertion process. Deuterium labelling experiments, kinetic studies and control experiments were carried out for the rationalization of the mechanism.