Thermal reactions of N-benzylidene- and N-(2-pyridylmethylidene)-tert-butylamines (5 and 13) under FVT conditions have been investigated. Unexpectedly, at 800 °C, compound 5 yields 1,2-dimethylindole and 3-methylisoquinoline. In the reaction of 13 at 800 °C, 3-methylimidazo[1,5-a]pyridine was obtained as the major product. Mechanisms of these reactions have been proposed on the basis of DFT calculations. Furthermore, UV-photoelectron spectroscopy combined with FVT has been applied for direct monitoring and characterization of the thermolysis products in situ.

Pyrrolopyridines and naphthyridines are formed by flash vacuum thermolysis (FVT) of 3‐ and 4‐pyridylmethylidene‐tert‐butylimines 8 and 15. Elimination of a methyl radical generates resonance stablized 2‐azaallyl radicals a1 and b1. The formation of pyrrolopyridines 9, 16 and 17 is rationalized in terms of cyclization of 1‐aziridinyl radicals a2 and b2. Formation of naphthyridine 10 from imine 8, and of 11 and 18 from imine 15, are in accord with cyclization of 1‐azaallyl radicals a6 and b9. Formation of naphthyridine 11 from 8, and of 10 and 19 from 15, indicate the operation of the spiro‐cyclization pathways forming intermediates a9 and b14. Formation of the 1,8‐naphthyridine 20 (3 %) indicates a rearrangement through aziridine b22 and biradical b23. DFT calculations at the CAM‐B3LYP/6‐311G(d,p) level support the proposed reaction mechanisms.

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