1.2- Diazepines. rearrangement pyridazines

Stanovnik and co-workers (100,101) systematically investigated the cycloaddition reactions of diazoalkanes with unsaturated nitrogen heterocycles, such as azolo-[l,5-fl]pyridines, pyridazin-3(2/7)-ones, and [fo]-fused azolo- and azinopyridazines. The Stanovnik group have studied the further transformations of the products and reviews of this chemistry are available. In a typical example, the reaction of 6-chlorotetrazolo[l,5-/7]pyridazine (37) with 2-diazopropane yields the NH,NH-dihy-dro-pyrazolo[4,3-(i]tetrazolo[l,5-/7]pyridazine 38 (102) (Scheme 8.11). The latter substrate reacts with acetone to produce an azomethine imine 39 that thermally rearranges to give the fused dihydro-1,2-diazepine 40. The azomethine imine obtained with glucose can be trapped with methyl acrylate to furnish the C-nucleoside 41 (103). 

There are several examples of pyridazine formation from seven-membered precursors, in particular diazepines. 2-Tosyldiazepin-4-one rearranges in the presence of sodium alkoxide or cyanide ion in methanol to a pyridazine. The... 

The cyclization reaction of 39 under basic conditions furnished a 1 1 mixture of diazepines 40 and 43. The unexpected formation of 43 has been rationalized by a Smiles rearrangement involving a nucleophilic attack of the deprotonated 3 -nitrogen at position 4 of the second pyridazine ring resulting in the displacement of a carboxamide anion followed by cyclization to afford 43. ... 

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