Cyclopropene pyridazine addition

The addition of diazo compounds to cyclopropenes often gives diazabicyclo[3.1. OJhexenes which rearrange under more vigorous conditions to pyridazines or dihydropyridazines these reactions are discussed elsewhere (see Sections 1.A.1.1.6.1.5.3.1. and 1.A.4.2.1.1.2.). In some cases, however, the bicyclic systems cannot be isolated and a pyridazine is produced directly from a cyclopropene examples of such reactions are the formation of 1/33.134 2135-138 3 io4... 

The addition of diazoalkanes to methylene cyclopropenes gives pyridazines. A labile 1 1 adduct (41) was isolated in the case of diazoethane, thus indicating the reaction sequence leading to 42 as the product. ... 

Alkenes lead to 1,4-dihydropyridazines (347) or the spiro derivatives (348). Cyclic alkenes, such as cyclopropenes give rise to diazanorcaradienes (349) or higher homologues, and reaction with alkynes yields pyridazines (350). Hetero-27r-systems such as nitriles, imines, thioketones, and N-sulflnylamines open the way to heterocyclic six-membered systems (351), (353), (357), and (356). (4-1-1) Addition reactions of isocyanides and carbenes make isopyrazoles (354) and (355) available. Reduction processes lead to 1,4- or 1,6-dihydrotetrazines (340) or (352). The reactions of 1,4-dihydrotetrazines (340) were briefly collected in Scheme 57. 

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