With 2-hydrazinothiazoles

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... 

Condensation of 2-hydrazinobenzothiazoles with a variety of electrophiles leads to interesting intermediates in the synthesis of useful heterocycles <88BCJ1339>. In particular, the reaction of 2-hydrazinobenzothiazole with ethyl acetoacetate gives the corresponding pyrazolone (Scheme 43). An identical reaction takes place with 2-hydrazinothiazoles and 1,3-dicarbonyl compounds to give pyrazoles <88JHC543>. 

Isocyanate, Me, 431 phenyl, 431 Isocyanates, 58 acyl isocyanates, 92 alkyl isocyanates, 92, 118 aryl versus alkyl, 118 with hydrazinothiazoles, 100, 106 with 2-imino-4-thiazolines, 125 to mesoionic compounds, 65 to thiazolyl urea, 58, 92 Isoindolenine derivative, 56 Isomerism, E-Z equilibrium, 23 Isomerization, catalyst in aji-unsaturated acids, 438... 

Ketoesters, acylation with, 53 with hydrazinothiazoles, 102 Ketone, reactions with, A-2-thiazoline-5-ones, 432... 

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). 

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). 

Phenyl-2-thiazolylazo)benzene 277 reacts with Grignard reagents to yield the corresponding 2-hydrazinothiazole (521). 

Thiosemicarbazides (141), Rj = H, yield the 2-hydrazinothiazoles (Scheme 68). Compound 142, R] = H, on reaction with o-halocarbonyl... 

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). 

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

Hydrazinothiazole derivative 400 reacted with substituted benzoic acids to provide compounds 401 in good yields (Equation 77) <2004PS(179)1019>. 

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). 

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>. 

If the reaction of thiosemicarbazide with chloroacetone is carried out in a warm dilute solution of hydrochloric acid, the thiosemicarbazone of chloroacetone (242) is formed in 85% yield. Heating 242 in ethanol cyclizes it to thiadiazine 243, whereas heating in anhydrous ethanolic benzaldehyde yields the benzylidene derivative of 4-methyl-2-hydrazinothiazole (244). At the same time, refluxing 242 in concentrated hydrochloric acid gives rise to 4-methyl-3-aminothiazoline-2-imine (245) in 95% yield. The latter compound can be also obtained by the action of concentrated HCl on thiadiazine 243. On using various a-halogenoketones and thiosemicarba-... 

Hydrazinothiazoles (54CB1392) and 2-arylthiazolone-2-hydrazones (59JPR265) are recyclized into the corresponding 3-aminothiazoline-2-imines on heating with hydrochloric acid [Eqs. (59) and (60)]. 

Give the structures of the bicyclic compounds formed by the following reactions (i) 2-hydrazinothiazole with nitrous acid C3H2N4S (ii) 2-aminothiazole with BrCH2COPh —> C11H8N2S. 

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