Abstract
This paper reviews our nearly twenty-five years' activity on 1,2-diaza-1,3-butadienes and shows that these compounds are powerful tools in organic chemistry. In fact, α-substituted-, α-oxo-, and α,β-unsaturated-hydrazones, have been obtained from 1,2-diaza-1,3-butadienes, as have pyrroles, pyrazoles, imidazoles, thiazoles, selenazoles, 1,2,3-thiadiazoles, 1,2,3-selenadiazoles, pyridazines, pyrazines, 1,2,4-triazines, and mixed heterocyclic systems.
Highlights
This paper reviews our nearly twenty-five years’ activity on 1,2-diaza-1,3-butadienes and shows that these compounds are powerful tools in organic chemistry
This account deals with our contributions to the chemistry of compounds bearing an azo group adjacent to an aliphatic double bond (Figure 1)
Only a modest number of papers had appeared in the literature until this date
Summary
The chemical properties of DBD are related to: (i) the conjugated heterodiene system, and, (ii), the substituents on the carbon and nitrogen atoms. The hydrazone intermediates were not always isolable, in general three main reaction pathways are possible: (i) the production of α,β-unsaturated hydrazones when the attacking nucleophiles bear leaving groups (in particular cases, the carbon–heteroatom double bond formation was observed); (ii) heterocycle formation with “closing” groups on the attacking nucleophiles by different [2+2], [3+2], and [4+2] annulations; (iii) heterocycle formation with “closing” groups present on the former DBD molecule In these last two processes, both nitrogens can be operative (Scheme 2). Other collateral and/or subsequent reactions (i.e., oxidation of the carbon in the α-position to the hydrazono moiety, cleavage of hydrazino/hydrazono groups with production of α-substituted carbonyl compounds, cleavage of N–C and/or N–N bonds), enrich the chemistry of the title compounds These reactions do not require anhydrous solvents or inert atmospheres, and generally occur under mild conditions and need only simple work-up procedures.
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