Diazepine ring cleavage

With munchnones, the initial adducts (330) spontaneously lose carbon dioxide with ring cleavage to give the benzo-l,3-diazepines (331) (81TH50901). 

Hydrolytic cleavage of a seven-membered ring occurs in the metabolism of chlordiazepoxide (5.82, Fig. 5.22,a) and other benzodiazepines (see also Sect. 11.9). The lactam ring opened metabolite 5.83 was detected in humans and dogs and is believed to be generated by hydrolysis of the intermediate lactam [181][182], However, the diazepine ring can be split by other mech-... 

Contrary to the stable azepines and diazepines, benzo[ 7]benzofuro[2,3-/][l,4]-oxazepine 272 undergoes ring cleavage under reductive conditions in the acetic acid/acetic anhydride to afford open chain acetoxy amine 273 (Scheme 58, Section 3.2.2 (2001JHC383)). 

Ring cleavage occurred in the reaction of 3,5,7-triphenyl-4H-l,2-diazepine with Fe2(CO)9, resulting in the rupture of the N—N bond. The Mossbauer spectrum of the product Fe2(CO)g[N C(Ph)CHC(Ph)CH2C (Ph) N] showed the two iron atoms to be in different environments, which was confirmed by a subsequent X-ray crystal determination. Unequal F e—X distances were found (Ca), but the C—C distances in the chain bridging the two nitrogen atoms were found to be approximately the same rather than indicating the incorporation of a CHj unit (118). 

The thermolysis of l,5-diazabicyclo[3.3.0]oct-2-enes (170) (Equation (25)) also provides a relatively simple synthesis of 4,5-dihydro-l//-l,2-diazepines (171) and 5,6-dihydro-4//-l,2-diazepines (172) through ring cleavage or a [3 -I- 2]-cycloreversion, depending upon the substitution pattern of the bicyclic skeleton <82LA1741>. 

Reaction of 2-methyl-3-methoxy-2/f-l,4-diazepine with benzoyl chloride in pyridine at 0°C resulted in ring cleavage and the methyl ester of A -benzoylalanine was obtained <87CPB1179>. 

Substituents of the imino group and the pyridine ring exert an essential influence on the decomposition of the product (see Table V). 2- and 4-Monoalkylpyridine A-ethoxycarbonylimines also yield only diazepines, but the corresponding A-acetylimines156 furnish considerable amounts of N-N bond cleavage products (pyridine and methyl isocyanate). Irradiation of 3,... 

Various diazepines form pyridines by ring contraction. For instance, thermolysis of 1-ethoxycarbonyl-4-methyl-l//-l,2-diazepine 202 leads to 4-methylpyridyl-2-carbamate 204 by undergoing valence isomerization to diazanorcaradiene 203 followed by N-N cleavage with aromatization. In contrast. 

In another example, the hydrogenation of the azapenam (55,6/ )-6-methoxy-2,2,6-trimethyl-l,4-diazabicyclo[3.2.0]heptan-7-one (154), prepared by reaction of a pentacarbonyl chromium carbene complex with liV-Boc-4,4-dimethylimidazoline, in the presence of 1.1 equiv. of racemic camphor sulfonic acid resulted in the cleavage of the Boc group and ring expansion of the azapenam to hexahydro-3,3,6-trimethyl-6-methoxy-5//-l,4-diazepin-5-one (155) in 71% yield <92JA5010>. It was pointed out that the ready availability of a variety of substituted chromium carbene complexes and imidazolines would make this a general route to this class of diazepine. 

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