Alkylation of 2,3‐Dihydro‐1,4‐diazepinium Salts

N ‐Unsubstituted 2,3‐dihydro‐1,4‐diazepinium salts 4a – d are N ‐methylated readily (→ 5a – d ) by using iodomethane and potassium carbonate in dimethylformamide. The 2,3‐dihydro‐5,7‐diphenyl‐1,4‐diazepinium salt 4d could be N ‐ethylated but not N ‐isopropylated, presumably for steric reasons. Vicinal crowding between, 1,4‐alkyl and 5,7‐phenyl substituents at the dihydrodiazepinium ring is evident from NMR spectra. 2,3‐Dihydro‐6‐(hydroxyphenyl)‐1,4‐diazepinium salts ( 2a, b ) are methylated first at the nitrogen atoms (→ 1a, b ) and only then at the hydroxy group (→ 3a, b ).