Photoreaktionen von 5‐Phenyl‐pyrazolinen. Vorläufige Mitteilung

On irradiation in benzene 1‐methyl‐5‐phenyl‐Δ 2 ‐pyrazoline ( 1 ) is partly converted into trans ‐ and cis ‐1‐methylazo‐2‐phenyl‐cyclopropanes ( 2 and 3 ) in the ratio of 23:77. Both 2 and 3 on thermal treatment are reconverted to 1 . A concurrent thermal equilibration of 2 and 3 is also observed. 1, 3‐Dimethyl‐5‐phenyl‐Δ 2 ‐pyrazoline ( 5 ) on irradiation in benzene yields the corresponding trans ‐ and cis ‐1‐methylazo‐1‐methyl‐2‐phenyl‐cyclopropanes ( 6 and 7 ). In contrast similar treatment of 5‐phenyl‐Δ 2 ‐pyrazoline gives benz‐ and cinnamaldazine ( 9 and 11 ) along with the corresponding mixed aldazine ( 10 ).