2,2-(n,n′-dimethyl-ethylendiamino)-ethylendiazonium-ion,ein diazonium-ion mit ungewöhnlichen eigenschaften

On treating with potassium methoxide at room temperature the donor-substituted ethylenediazonium ion $\text{2}$ equilibrates with the stable α-diazoolefin $\text{3}$. At the same temperature the reaction of $\text{2}$ with dilute methanesulfonic acid leads to a quantitative elimination of diazo nitrogen. Finally the 1,3-dipolar cycloaddition of $\text{2}$ to dimethyl acetylenedicarboxylate affords the pyrazole derivative $\text{5}$ in high yield.