Of A-2-thiazoline-4-one

Recently, Koitai et al. (17) have shown that 5,5-diphenyl-2,4-thiazolidinedithione (15) with aluminum chloride in refluxing toluene gives 4,5-diphenyl-A-4-thia2oline-2-thione (16) (Scheme 7). 3-Methyl-4,5-diphenyl (17) and 4,5-diphenyl-A-4-thia2oline-2-thiones (16) are obtained in very low yields (1 to 5%) as by-products of the reaction between deoxybenzoin. benzoin. l,2-diphenyl-1.2-ethanediol. 1.2-diphenylethanol, or benzil, and Sg in hexamethylphosphoamide (18), The transformation of A-4-thiazoline-2-ones to the corresponding thiones by P2S5 (19) is of little synthetic value since the latter are more easily prepared. 

A-4-Thiazoline-2-ones and ring substituted derivatives are usually prepared by the general ring-closure methods described in Chapter II. Some special methods where the thiazole ring is already formed have been used, however. An original synthesis of 4- 2-carboxyphenyl)-A-4-thiazoline-2-one (18) starting from 2-thiocyanato-2-halophenyl-l-3-indandione (19) has been proposed (Scheme 8) (20, 21). Reaction of bicyclic quaternary salts (20) may provide 3-substituted A-4-thiazoline-2-one derivatives (21) (Scheme 9) (22). Sykes et al. (23) report the formation of A-4-thiazoline-2-ones (24) by treatment ef 2-bromo (22) or 2-dimethylaminothiazole (23) quaternary salts with base (Scheme 10). 

Physical properties of A-4-thiazoline-2-one and derivatives have received less attention than those of A-4-thiazoline-2-thiones. For the protomeric equilibrium, data obtained by infrared spectroscopy favors fbrm 51a in chloroform (55, 96, 887) and in the solid state (36. 97. 98) (Scheme 23). The same structural preference is suggested by the ultraviolet spectroscopy studies of Sheinker (98), despite the fact that previous studie.s in methanol (36) suggested the presence of both 51a and... 

The infrared spectra of A-4-thiazoline-2-ones are characterized by a strong absorption around 1650 cm (55, 86, 103, 107. 870). For the N-H derivatives, the whole range 2700 to 3200 cm is covered by a strong absorption related to the dimeric and oligomeric states of the hydrogen-bonded structures (85, 86). 

The charge diagram of A-4-thiazoline-2-one is summarized in Table VII-9. This diagram and the one obtained by a HMO treatment (105) are consistent with the easy acetylation occurring in position 5 of the ring. However, PPP calculations indicate that this electrophilic substitution could also have occurred in position 4, which is not observed. 

Alkylation of A-4-thiazoline-2-one may yield O-R or N-R derivatives according to experimental conditions. With diazomethane in ethanol O-raethylation takes place (29. 36. 214). N-Methylation is reported when a basic solution of A-4-thiazoline-2-one reacts with methyl iodide or dimethylsulfate (21, 29, 215, 216), Reaction of l-chloro-2-dimethyl-aminoethane with the sodium salt of 4 R-A-4-thiazoline-2-one (91) in alcohol, first claimed to yield the aminoalkylether (217, 218), was shown after infrared investigation to give the N-substituted derivative (92) (107), even when R Ph (Scheme 45). More probably the site of reaction in... 

Reaction of (EtOfsPOCl with the sodium salt of A-4-thiazoline-2-one (93) in dry acetone provides the corresponding diethyl thiazolyl-2-phosphate (94) (Scheme 46) (220-223). (EtO) PSCl reacts in the same way with various A-4-thiazoline-2-ones (224-227). When phosphoryl chloride is used the reaction goes further, and 2-chlorothiazole is obtained (7, 193, 194, 217, 228-2.30). 

Reduction of A-4-thiazoline-2-one by zinc dust gives low yields of the corresponding thiazoles (36, 231). The formation of thiochrome (95) results from an intramolecular nucleophilic attack (Scheme 47) (232). 

Diazomethane alkylation of A-4-thiazoline-2-ones (36, 214) or the Williamson reaction of 2-halogenothiazoles (6. 287-300) provide good yields of 2-alkoxythiazole otherwise obtained by reaction between O-esters of monothiocarbamic acid with a-halocarbonyl compounds (see Chapter II). 

TABLE VII-13. USES OF A-4-THIAZOLINE-2-ONES AND A-4-THIAZOLINE-2-THIONE DERIVATIVES... 

Acylation of A-4-thiazoline-2-one, 402 Acyl-2-imino-4-thiazolines, reduction of,... 

Iodide, 121 Iodination, 77 of A-4-thiazoline-2-one, 402 Iodine, as catalyst of rearrangement, 406 Ionization potential, relation with nucleophilic reactivity of A-4-thiazoline-2-thione, 384... 

Uses, aminothiazoles derivatives, 132-172 hydroxythiazole derivatives, 438-442 mercaptothiazole derivatives, 438-442 UV spectra, 21 of alkylaminothiazoles. 38 and amino-imino equilibrium, 19, 20 and charge transfer, 21 of iminothiazolines, 38 and PPP calculations, 21 and potentiometric measurements, 21 representative data, 22 of Schiff bases, 41 and solvent effects, 21 and substituent effects, 22 of sulfathiazoles, 20 -of sulfonamidothiazoles, 116 of A-2-thiazoline-4-one, 422 pKa determination, 423 of A-4-thiazoline-2-one, in relation with protomerism, 387 representative data, 389 of A-4-thiazoline-2-thiones, 380. 381 in relation with protomerism. 378 of thiazolylcarbamates, 97 of thiazolyl-2-oxides, 409 of thiazolyl-4-oxides, 426 of 2-thiazolylthioethers, 404 of thiazolylthioureas, 94, 96 of thiazolylureas, 93... 

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