Pyrolysis of 1-substituted pyrazoles and chloroform at 550 °C: formation of α-carboline from 1-benzylpyrazoles

Pyrolysis of 13CH3 labelled 1-methylpyrazole 8 with chloroform at 550 °C in a continuous flow reactor yields unlabelled 2-chloropyrimidine 9 and 2-cyanopyrrole 10 labelled at the cyano group. However, pyrolysis of 1-benzylpyrazole 14 with chloroform under similar conditions gives 9, 2-phenylpyrimidine 13 and, as the major product, α-carboline 15. Pyrolysis of several substituted 1-(arylmethyl)pyrazoles and the use of 13C and 15N labelled compounds provides direct evidence by which the positions of 7 atoms of 1-benzylpyrazole can be located in the α-carboline. These data support the mechanisms suggested for the formation of 9, 10, and 15.