v‐Triazolines, XXIV. Pyrazolecarbaldehydes from 5‐Amino‐4,5‐dihydro‐4‐methylene‐v‐triazoles and Sydnones

The sydnones 1a–c react with the 4,5‐dihydro‐v‐triazoles 2a–c by long refluxing at 110– 140°C affording via non‐isolable adducts with elimination of CO2 and N2 and rearrangement a mixture of 4,5‐dihydropyrazoles 3a– c, 3‐pyrazolecarbaldehyde anils 4a–d, and 3‐pyrazolecarbaldehydes 5a–c. Compounds 3 can be deaminated to give 4 which can be hydrolyzed to yield the 3‐pyrazolecarbaldehydes 5.– The sydnones 6a, b react similarly with 2a to give a mixture of 4‐pyrazolecarbaldehyde anils 7a, b and 4‐pyrazolecarbaldehydes 8a, b. The structural assignments are based on spectroscopic and X‐ray diffraction data.