Diazepines. Part 25. Preparation and properties of 6-aryl-2,3-dihydro-1,4-diazepinium salts. Electronic interaction between the rings and steric inhibition thereof

Abstract

A variety of 6-aryldihydrodiazepinium salts (including also 6-biphenyl-4-yl, 6-α-naphthyl, and 6-N-pyridyl) has been prepared, mostly by reactions of 1,2-diamines with 3-aryl-1,5-diazapentadienium salts. The electron-rich dihydrodiazepinium cation activates the 6-aryl substituent towards electrophilic attack, and halogenation and nitration take place at the p-position. Substituents vicinal to the ring junction in either the six- or seven-membered rings inhibit this reactivity, presumably by preventing coplanarity of the two rings; the ¹³C n.m.r. spectra of these vicinally substituted compounds also show the lowered electronic interactions between the rings. NN′-Diphenyl and NN′-dibenzyl substituents also inhibit electrophilic substitution in the 6-phenyl ring. Solution in deuteriosulphuric acid generates a stable radical species. Nucleophiles (monoamines, diamines, sodium hydroxide) attack the 5-and 7-positions of the diazepine ring. The ¹³C n.m.r. and mass spectra of these compounds are discussed.