Reactive intermediates. Part XXI. Thermal ‘decarboxylation’ of 2,6-diazatricyclo[5,2,1,0]deca-4,8-diene-3,10-diones to pyrazolo[1,5-a]-pyridines

Abstract

Oxidation of pyrazolin-5-ones (1) in the presence of tetraphenylcyclopentadienone gives high yields of 2,6-diazatricyclo[5,2,1,0]deca-4,8-diene-3,10-diones (12). On heating, the latter give pyrazolo[1,5-a]pyridines (13) and carbon dioxide formed from two non-adjacent carbonyl groups. A mechanism is proposed for this unusual rearrangement, which is paralleled in the mass spectrometer.

Oxidation of 3,4-diphenyl-Δ²-pyrazolin-5-one (1; R¹= R²= Ph) with lead tetra-acetate in methanol gives methyl cis-3-methoxy-2-phenylcinnamate (8), and in ethanol gives ethyl cis-3-ethoxy-2-phenylcinnamate.