First reactions of dialkoxycarbenium tetrafluoroborates with pyrroles, 5H‐dibenz[b,f]azepines, and electron‐rich arenes

Pyrrole (2a) and 2,5‐dimethylpyrrole (2b) react with the dialkoxycarbenium tetrafluoroborates 1a‐1c under kinetic control to yield the corresponding acylpyrrole derivatives. 5H‐Dibenz[b,f]azepine (9a) and the 10,11‐dihydro derivative 9b react only with the most electrophilic of the series of electrophiles tested, namely, diethoxycarbenium tetrafluoroborate (1a), to furnish the corresponding formyl derivatives. Similarly, in arene chemistry, the highly electron‐rich N,N‐dimethylaniline (13a) and 1,3,5‐trimethoxybenzene (13b) are formylated by reaction with 1a.