First N ‐Functionalization of 4‐Nitroso‐1 H ‐Pyrazoles Using Monofunctional and Bifunctional Alkylating Agents

Abstract The direct N ‐alkylation reactions of ambident 3,5‐substituted 4‐nitroso‐1 H ‐pyrazoles are described for the first time. An efficient method of the 4‐nitroso‐1 H ‐pyrazoles and their sodium alkyl‐, allyl‐ salts regioselective N ‐alkylation by benzyl halides, halocarboxylic acids esters, and related bifunctional alkylating agents is established with the use of superbasic conditions or reflux in acetone. A series of new N ‐functionalized nitrosopyrazoles and bis(4‐nitrosopyrazole) compounds is successfully obtained with a yield of up to 85 %. Using quantum‐chemical calculations, it is shown that in terms of kinetics and thermodynamics, the N ‐alkylation of the considered pyrazoles is a more advantageous process than O ‐alkylation.