1.2- Diazepines from pyrylium salts

H-1,2- Diazepines acylation, 7, 602 nucleophilic reactions, 7, 603 protonation, 7, 601 from pyrylium salts, 3, 660 4-subs tituted synthesis, 7, 604 synthesis, 7, 598, 599 thermal reactions, 7, 600... 

The 1,2-diazepines (41 and = Me, Ph, etc.), obtained from the reaction of hydrazine with pyrylium salts, have been shown to give 1,4-diazepines (42) on photolysis, while pyrolysis of the diazanorcaradienes (43) gives the 1,2-diazepines (44), presumably via the intermediate (45). In a related case, thermolysis of (46) caused conversion into a 1,3-diazepine (47), for which a mechanism has been presented. ... 

From reviewing the literature for the synthesis of 1,2-diazepines, just from the volume of the work it is apparent that the most preferred route to make 1,2-diazepines, starting from fragments, has been the type bg approach by using a 1,5-dielectrophile with hydrazine (a 1,2-nucleophile). In the case of ring transformation approach to 1,2-diazepines, the conversion of a pyrylium or a thiapyrylium salt to 1,2-diazepines has been the preferred route. In the end, the preferred method would depend on the nature of substituents and the unsaturation required on the 1,2-diazepine ring. 

---