Diaminomethylation of Pyrazoles

Abstract

AbstractWe studied the reaction of N‐alkyl(aryl)pyrazoles with silylformamidine 1 that exists in an equilibrium with its carbene form via migration of the trimethylsilyl group from the carbon to nitrogen atom. The carbene insertion proceeded at the C−H group in 5th position. N‐alkyl(aryl)pyrazoles featuring substituents such as Br, CN and NO2 group reacted readily affording the corresponding aminals. This approach allowed us to synthesize pyrazole dialdehyde and phosphine featuring a vicinal aldehyde group. The reaction does not require any catalyst. The insertion position was unambiguously confirmed by X‐ray analysis of an aminal and a set of derivatives. Aminals hydrolysis afforded the corresponding pyrazole carbaldehydes. Methanolysis of the aminals gave N‐methylimines of the pyrazolecarbaldehydes. Highly acidic nitro pyrazole instead of the insertion underwent silylation in 5th position.