Carbonyl-activated diazo compounds and enamines (acyclic or with a six-membered ring) undergo 1,3-dipolar cycloaddition. The invariant orientation of the reactants is remarkable: the initial products are 4-aminopyrazolines such as (1). In contrast, the (partly isolable) zwitterions (2) formed as primary products from enamines with a five-membered ring arise by azo coupling.
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Huisgen et al. (1979) studied this question.
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