Some dihydrodiazapepinium salts and related compounds.

Abstract

A wide variety of 6-aryl-2, 3-dihydro-1, 4-diazepinium salts has been prepared by reaction of 1,2-diamines with 1, 5-diaza-3- aryl-pentadienium salts. The latter compounds were readily accessible by Vilsmeier formylation of the appropriate arylacetic acid. Some dianil salts were also prepared via chlorovinyl- aldehydes.

Cyclisation of the 3-aryl substituted vinamidinium compounds is sensitive to the effects of substituents adjacent to the reactive centres. The reaction of the open-chain vinamidinium salts with piperidine suggests that the formation of the 7-membered ring compounds is a two step process, with the rate of cyclisation determined by the second-step. For sterically hindered aryl-vinamidinium salts and/or diamines cyclisation to diazepines was accomplished either by initial treatment of the vinamidinium salt with ammonia followed by addition of the diamin or by using the sodium salts of arylmalondialdehydes obtained by alkaline hydrolysis of the vinamidinium salts.

Some 6-unsubstituted dihydrodiazepinium salts were also prepared from β-diketones.

The studies of the reactions of 6-aryl-2, 3-dihydrodiazepinium salts with electrophiles showed that bromination and nitration occurs at the p-position of the 6-phenyl ring, and that the phenyl ring is activated by its diazepine substituent. A substituent adjacent to the bond linking the two rings alters the geometry of the two rings and consequently affects the chemistry of these compounds by diminishing the conjugation between the two rings.

Kinetic studies indicate that substituents at the 2-position and N-positions of the diazepine ring also affect reactions at the P-position of the 6-phenyl ring; the rate of bromination is lowered by the introduction of methyl substituents at the 2-position.

The halogen atom of a 6-(p-halogenophenyl) dihydrodiazepinium salt is not replaced by nucleophiles. 5, 7-Unsubstituted-6-aryl- dihydrodiazepines undergo 'transdiazepination' on treatment with substituted ethylenediamine.

The 6-phenyldihydrodiazepinium salt forms a free radical on addition of concentrated sulphuric acid.

The mass spectral fragmentation of these compounds indicates the primary loss of an N₁-C₂ species; other fragmentation patterns are also described.

Some 1, 5-benzodiazepines were also studied. They also contain the vinamidinium system, but it is perturLed by a complicated interaction between the two rings. Bromination of these compounds takes place at the 2, 4-methyl substituents. Their mass spectra differ from those of the 6-aryldihydrodiazepines; quinoxaline and benzimidazole species are the predominant breakdown products. Some simple macrocycles were prepared from β- diketones and diamines. They also differ from the 2, 3-dihydro- diazepines; for example no electrophilic substitution products could be isolated.

The effect of electronic perturbation on the 1, 5-diazapenta- dienium system when it is contained in 1, 2-dihydro-2-oxo- and 2-thioxo-5-arylpyrimidinium salts was also investigated. They formed adducts with piperidine at their 4-position. Their syntheses were carried out by reactions of arylmalondialdehydes with dimethyl substituted urea and thiourea. Some of these compounds showed fluorescence. The electronic structures of 2, 3-dihydro-6-aryl-1, 4-diazepinium salts, and of the other related salts containing the vinamidinium system which are considered in this thesis, were investigated by ¹³C n.m.r. spectroscopy.