2-Hydrazinothiazoles hydrazine

This set of compounds is the most thoroughly studied among derivatives of 2-aminothiazole, thanks to the Beyer group. Heterocychzation methods are most commonly used for their preparation (see Chapter II and Refs. 37, 341, and 513-520). Reaction of 2-diazothiazoles (277) with organometallics provides another synthetic method (Scheme 1711 (521). 2-Hydrazinothiazoles may also be obtained by the action of hydrazine on 2-bromothiazoles (388) or on 2-mercaptothiazoles (522). 

The principal reactions of this class of compounds are summarized in Scheme 172. In most of these reactions the reactive nucleophilic center is the terminal NHj group, although the other exocyclic nitrogen may also be involved, as shown by acetylation, which yields 284 and 285. However, the structure of compound 281 is not the one proposed in a recent report (1582) that attributes the attack to the other exocyclic nitrogen. The formation of osazones (287) from sugars, 2-hydrazinothiazoles, and hydrazine has been reported (525, 531). 

Thiazolopyranopyrazoles such as 438 were obtained from condensation of hydrazinothiazoles 436 with activated cinnamonitriles 437 followed by further reaction with hydrazine (Equation 118) <1998JRM3207>. 

A new efficient procedure has been proposed for the synthesis of 3-aryl-5-amino-l//-pyrazoles by reaction of a-chloro-/ -arylacrylonitriles with hydrazine hydrate <2004RJ01518>. Reaction of 2-(3,3-dicyano-2-propenylidene)-4,4,5,5-tetra-methyl-l,3-dioxolane 641 with hydrazine afforded 3-(2-hydroxy-l,l,2-trimethylpropoxy)pyrazole 642 (Equation 134) <2003RJ01016>. Treatment of ethyl 3,3-dicyano-2-methoxyacrylate with alkyl, aryl, heterocyclic, and sulfonyl hydrazines led to the synthesis of N-l-substituted 3-acyM-cyano-5-aminopyrazoles, which are versatile intermediates for the synthesis of many biologically active scaffolds <2006TL5797>. 2-Hydrazinothiazol-4(5//)-one reacted with a variety of cinnamonitrile derivatives and activated acrylonitriles to yield annelated pyrazolopyrano[2,3-rf thiazole <1998JCM730>. 

---