2,3-Dihydro-l ,4-diazepines

Diaminoethane reaets with diaeetylene (0-25°C, 4 h) to form a mixture of tautomers of 5-methyl-2,3-dihydro-l,4-diazepine (4) isolated by sublimation (yield not reported) (69JOC999 77ZC216). 

The reaction of l-dialkylaminobut-l-en-3-ynes 100 with 1,2-diaminoethane (80°C, H" ", 2 h) leads to a mixture of 5-methyl-2,3-dihydro-l,4-diazepine tautomers (4) (the most stable tautomers are shown) (83ZOR1541). 

Throughout this article, the terms dihydrodiazepine and dihydro-diazepinium are used exclusively to refer to 2,3-dihydro-l,4-diazepines (1) and their monocations (2), respectively. Spectroscopic data show that the dihydrodiazepines normally exist in the conjugated form (1) rather than in the tautomeric bisimino form (3). 

Volume 56 of Advances in Heterocyclic Chemistry consists of four chapters. Drs. Douglas Lloyd and Hamish McNab from Scotland have provided an updated account of the chemistry of 2,3-dihydro-l,4-diazepines, a subject which has not been specifically reviewed for eighteen years and one with which these authors have been intimately concerned. 

Treatment of a solution of 2,4-dimethylbenzodiazepine in benzene with gaseous DC1 led to N-deuteriation but no C-deuteriation (63JA3354). There is an implication here that H/D exchange does not take place at C-3, as happens in 2,3-dihydro-l,4-diazepines, for traces of either the tautomeric... 

The lack of bromination at the 3-position is in stark contrast to the extremely ready bromination at the 6-position (analogous to the 3-position in benzodiazepines) of 2,3-dihydro-l,4-diazepines or -diazepinium salts [93AHC(56)1]. The latter compounds possess, respectively, vinamidine or vinamidinium systems, which are readily susceptible to halogenation at the central carbon atom. In contrast to these dihydrodiazepines, 1,5-benzodi-... 

In several synthetic studies, cyclopropane derivatives were used as synthones or building elements for ring enlargement steps, e.g. reaction of enamines with cyclopropenone [65], synthesis of 2,3-dihydro-l,4-diazepine by thermal isomerization of 1,2-diamino-cyclopropanes [32] [66], and preparation of 3-amino-fulvenes from methylencyclopropenes with alkynamines [67]. 

A novel preparation of the 1,4-diazepine system (174) has been reported through isomerization of the Schiff base (175).186,187 This same type of diazepine (176) was prepared by the reaction of acetylacetone and meso-l,2-diphenylethylenediamine.188 Spectroscopic studies indicated that it was in the form shown. The NMR spectra of these 2,3-dihydro-l,4-diazepines and their cations have been discussed.187 The Schiff base of benzaldehyde and 1,2,3-triaminocyclopropane also isomerizes to give 174 (R = C6H5, R = C6H6CH=N).186 187,189 The mass spectrometric fragmentation of compounds of the type 176 has been reported.180a... 

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