Bridgehead nitrogen heterocycles—II: The mass spectra of some pyrazolo[1,5-a]pyridines

Pyrazolo1,5-a]pyridine undergoes fragmentation upon electron-impact by loss of HCN or C₂H₂N·. In the 2,3-dimethyl derivative loss of HCN and CH₃CN were both observed from the M – 1]⁺ ion and, in the 3-methyl-2-phenyl derivative, loss of PhCN occurred from the corresponding M – 1]⁺ ion. Loss of methyl and phenyl radicals was also observed. In 3-acetyl-2-methyl and 3-benzoyl-2-phenyl derivatives, characteristic losses of the CH₃CO· and PhCO· groups were noted. The introduction of a 7-methyl substituent into the six-membered ring had little effect on the fragmentation pattern.