Of 2-hydrazinothiazoles

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

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). 

Thiazolotriazepines (290) are prepared by reaction in cold pyridine of the product resulting from nucleophilic attack of I-hydrazinothiazole on... 

Oxidation of 2-hydrazinothiazoles with FeCls gives 2-azothiazoles in good yields (515, 521, 538-540). This oxidation may also be performed with dilute nitric acid (523, 541). However, the reaction of concentrated... 

The benzidine-like rearrangement of 2-hydrazinothiazoles has been observed by the Beyer group (523, 546). This rearrangement may be very fast (539). but does not occur with 2.2 -hydrazothiazole (300). where the... 

Hydrazinothiazoles form stable complexes with Mn ", Ni. Cd Cu ", Co ", Fe ", and Fe " this property was used to detect small amounts of these salts in mixtures by paper chromatography (547, 548). Some infrared features of the complexes formed with the silver salts and with the mercuric salts have been reported (1583). 

Alkylidenehydrazinothiazoles (297) can be prepared either from 2-hydrazinothiazoles (549) or by direct heterocyclization (527). Their characteristic infrared bands have been reported (550). The main mass spectrometric peaks of (4-coumarinyl-2-thiazolyl)hydrazone (302) (Scheme 179) (134, 551) are situated at mle = 361. 244, 243, 118, 216, 202, 174, 117 the proposed interpretation of the fragmentation pattern should, however, be reconsidered. Scheme l80 summarizes some representative reactions of this class of compounds. 

Under acidic conditions, a thiosemicarbazone intermediate (145) has been isolated, this can be cyclized in alcohol either into the corresponding 2-hydrazinothiazole (142) in the presence of benzaldehyde or into 1,3,4-thiadiazine (146) in the absence of benzaldehyde (Scheme 71) (375, 397, 408). 

Thiosemicarbazones of the general formula 155 react either with a-halocarbonyi compounds (59, 60, 67, 69, 71, 107, 743, 744, 788) or with 1-chloro-1,2-epoxides (504) to yield the corresponding 2-hydrazinothiazoles (156) (Scheme 78 and Tables 11-22 and 11-23). 

Rearrangement of 2-hydrazino-4-methylthiazole (291) to 2-amino-5-methyl-l,3,4-thiadiazine (296) in acidic medium has been reported (514. 531). We suggest that this reaction occurs by way of the retro-Hantzsch mechanism (Scheme 175). In this mechanism, a succession of reversible steps leads to the open-chain product (294), which can either revert to the starting product (291) or react further to give the thiadiazine (296). The whole reaction is expected to be reversible through this mechanism. The reaction would proceed from thiadiazine to 2-hydrazinothiazole if the 4-nitrogen atom and the 5-carbon atom of the thiadiazine were both substituted with bulkyl alkyl groups (343, 537). 

Nitroresorcinol, coupling with, 112 Nitrosation, 72-75 and diazotization. 65, 67 of 2-imino-4-thiazolines, 125 mechanism of, 68 of secondary amines, 68 Nitrosoimino-4-thiazoline, 126 Nitrosulfonamides, oxidation of, 115 Nitrous acid, with 2-hydrazinothiazoles, 100 1SC-NMR spectroscopy, representative data, in A-4-thiazoline-2-one. 390... 

Hydrazinothiazoles, synthesis of, from thiosemicarbazides and a-halo-caibonyl compounds, 251, 256... 

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>. 

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