Photochemisches Verhalten von 3,4‐Diarylsydonen . Vorläufige Mitteilung

3, 4‐Diphenyl‐sydnone ( 1a ) and 3‐ p ‐tolyl‐4‐phenyl‐sydnone ( 1b ) on irradiation with a mercury high‐pressure lamp in pyrex vessels yield 2,4,5‐triphenyl‐ ( 3a ) and 2‐ p ‐tolyl‐4,5‐diphenyl‐1,2,3‐triazole ( 3b ), respectively. Irradiation of 1a and 1b in the presence of dimethyl acetylene‐dicarboxylate or indene leads to the formation of the pyrazoles 4a and 4b and the Δ 2 ‐pyrazolines 5a and 5b , respectively. Reactive intermediates of the photoreaction of 1a and 1b seem to be the diazirines 2a and 2b , which open to give the 1,3‐dipolar structures 8a and 8b .