A number of possible synthetic routes to monocyclic, fully unsaturated 1,3-diazepines are reported.
Diazabicycloheptanones were prepared from the addition of dimethylsulphoxonium methylide to alkylated pyrimidones and attempts were made to expand the products to 1,3—diazepines. An interesting byproduct from one reaction was a novel sulphoxonium ylid. Three ispyrimidonylethanes were isolated from the alkylation of 2-thiomethyl-4-(3H)-pyrimidone with dibromoethane.
Derivatives of cis-2-aminocyclopropane-carboxylic acid were synthesized as precursors for diazabicycloheptanones. Many reactions of these derivatives resulted in opening of the cyclopropane ring.
Photochemical 2+2 cycloadditions of various alkenes to
1,3-disubstituted-2-imidazolones were performed. No diazabicycloheptanones were obtained. When dichloroacetyl chloride or trichloroacetyl chloride (precursors to dichloroketene) were reacted with these imidazolones, the products formed were not the expected cyclobutanone derivatives, but C-acyl derivatives of the starting material.
Modification of existing 1,3-diazepines synthesized from 4-chloromethyltetrahydropyrimidines led to the isolation of methyl 2,3,6,7-tetrahydro-l-benzyl-4-methyl-2-oxo-l,3-diazepine-5-carboxylate. The silylated derivatives of the 4-chloromethyltetrahydropyrimidines were unstable.
The reaction of 1,2,3-triazolo[1,5-a]pyridine with bromine gave 2-dibromomethylpyridine which was subjected to flash vacuum pyrolysis and treated with strong base. No products characteristic of pyridyl carbene were formed but 1,2-bis-(2-pyridyl)ethylene was obtained. A radical mechanism is proposed for this reaction. The proposed steric hindrance theory to explain the products obtained from the bromination of different triazolopyridines is described and tested.