Photochemistry of organic nitrogen compounds. Part II. The photolysis of pyrazolenines via diazo-compounds

Abstract

Evidence is described which throws further light on the mechanism proposed for the photolytic conversion of pyrazolenines into cyclopropenes. The intermediate diazo-compound from the photolysis of 3-(1′-hydroxy-1′-methylethyl)-5,5-dimethylpyrazolenine has been studied spectrophotometrically and by trapping with acetic acid. In the presence of acid, protonation initiates a pinacolic deamination sequence, and a hydroxy-ester and an epoxide are formed in comparable amounts. The epoxide is also a minor product of photolysis in absence of acid.

A one-step synthesis of 5,5-dimethyl-pyrazolenines is described.