The reaction of acetylenes with aldazines in the NaOBut/DMSO system: a contribution to the pyrazole chemistry

Arylacetylenes readily react with aromatic aldazines in superbase medium NaOBu^t/DMSO (1 vol% EtOH) at room temperature to afford mainly 4-arylmethyl-3,5-diaryl-1H- pyrazoles in up to 47% yield along with minor amounts of 1-arylmethyl-3,5-diaryl-1H-pyrazoles and 1,2-diaryl-1,2- bis(3,5-diaryl-1H-pyrazol-1-yl)ethanes. The reaction is rationalized as proceeding via the diazaallyl anions, the adducts of acetylenic carbanions to a C=N bond, which further undergo the proton transfer processes and intramolecular cyclization to the above pyrazole derivatives.