1,3-Dipolar cycloaddition reactions of diazoalkanes. Part II. Kinetics of the thermal and photochemical formation of pyrazole from diazopropene

Abstract

The spontaneous rearrangement of diazopropene to pyrazole is made faster by irradiation, but the corrected photorate is only approximately three times greater than the thermal rate at room temperature. Using filters it was shown that the wavelength of the activating light was 3100–3800 Å. Since the diazo-compound is transparent in this region it cannot be the primary absorbing species. It is suggested that the primary photochemical process involves the expected pyrazolenine intermediate.