Hydrazine and ring

Heterocyclics. One of the most characteristic and useful properties of hydrazine and its derivatives is the ability to form heterocycHc compounds. Numerous pharmaceuticals, pesticides, explosives, and dyes are based on these rings. A review of the appHcation of hydrazine in the synthesis of heterocychcs is available (91). For further information in the field of heterocycHc chemistry, see the General References. 

Pyrazolines can be prepared from the reaction between a hydrazine and two carbonyl compounds, one of them having at least one hydrogen atom a to the carbonyl group. Formally, these reactions correspond to the [NN + C + CC] class. However, if one considers the different steps in the ring formation, they more properly belong to the [CNN + CC] (Section 4.04.3.1.2(ii)), the [CCNN + C] (Section 4.04.3.1.2(i)), or the formation of one bond (Section 4.04.3.1.1) classes. 

There are two methods for the introduction of a hydroxyalkyl group at position 5 of the pyrazol-3-one ring. Schmidt and Zimmer converted furanediones 258a-k into arylmethylenepyrazol-3-reaction with hydrazine hydrate or methylhydrazine (83Jmechanism proposed for the reaction involves nucleophilic attack of the hydrazine on the ketone carbonyl, followed by attack on the ester carbonyl and ring opening of the... 

In a recent review of heterocyclic compounds no further mention is made of the three-membered ring structures for the condensation products from hydrazine and carbonyl compounds. However, the products obtained from azodicarbonyl derivatives with aliphatic diazo compounds were formulated as diaziridines [Eq. (1)]. Recent investi-... 

The potential of such reaction sequences for the generation of molecular diversity was also demonstrated by the synthesis of a library of heterocycles. Epoxide ring-opening with hydrazine and subsequent condensation with (3-diketones or other bifunctional electrophiles gave rise to a variety of functionalized heterocyclic structures in high purity [34]. A selection based on the substrate derived from cyclohexene oxide is shown in Scheme 12.12. 

Addition of nucleophiles to the cyano group of cyanothiadiazole under basic conditions takes place with unusual ease <88AG(E)434,94ACS372). Hydrolysis to the amide, for example, can be effected at 0°C in the presence of a catalytic amount of sodium hydroxide or basic ion-exchange resin. At reflux temperature, hydrazine and monosubstituted hydrazines convert 3,4-dicyano-l,2,5-thia-diazole into the l,2,5-thiadiazole[3,4-. The base-catalyzed addition of acetone to cyanothiadiazole forms an enamino ketone, used as a key intermediate for the synthesis of a number of heterocyclic ring systems, e.g. isothiazole, isoxazole, pyrazole, pyrimidine, and thiazole <77H(6)1985>. 

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