New Reactions of N-tert-Butylimines; Formation of N-Heterocycles by Methyl Radical Elimination on Flash Vacuum Thermolysis of N-Benzylidene- and N-(2-Pyridylmethylidene)-tert-butylamines

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. Hot rearrangement: Flash vacuum thermolysis (FVT) of N‐benzylidene‐ and N‐(2‐pyridylmethylidene)‐tert‐butylamines resulted in unexpected rearrangements (see scheme). At 800 °C, 1 gave 1,2‐dimethylindole (2) and 3‐methylisoquinoline (3) as the main products, whereas 4 afforded 3‐methylimidazo[1,5‐a]pyridine (5) in high yield. A combination of FVT with UV‐photoelectron spectroscopy was used to monitor the thermolysis products in situ.