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 CO 2 and N 2 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.