2- thiazole, acylation

Thiazoles, 2-acyl-, 13 formylation of, 73 halogeno-, 296, 347, 348 nucleophilic substitution of, 370... 

In another approaeh [88IJC(B)570], reaetion of 2-mereapto-4,5-di-p-tol-ylimidazole 43 with a-halo carboxylie acids enabled the synthesis of several imidazo[2,l-h]thiazoles. Acylative ring closure of 4,5-di-p-tolylimidazo-2-thioacetic acid (44, R = H) or 2-thiopropionic acid (44, R = Me) provides 5,6-di-p-tolylimidazo[2,l-h]thiazole-3(2//)-one (45, R = H) or its 2-methyl analog (45, R = Me). The synthesis of annelated imidazo[2,l-h]thiazoles (e.g., 46) can be achieved in one step by reaction of 2,3-dichloroquinoxaline with 43. The intramolecular eyelization of l-vinylimidazole-2-thiones to 2,5-dimethyl-3,6-arylimidazo[2,l-h]thiazoles with excellent yield has been reported (93T6619). 

The condensation of thioacetic acid with amino acids under drastic conditions provides a useful new synthesis of thiazoles (Scheme 146) (668, 669). Instead of the amino acid, Af-acyl <279) or N-thioacylamino acids (278) are used. 

Although in general azoles do not undergo Friedel-Crafts type alkylation or acylation, several isolated reactions of this general type are known. 3-Phenylsydnone (120) undergoes Friedel-Crafts acetylation and Vilsmeier formylation at the 4-position, and the 5-alkylation of thiazoles by carbonium ions is known. 

The dimethylsulfonium ylide (568) added readily to aroyl isocyanates to give the intermediate addition product (569). This on heating underwent ring closure with loss of dimethyl sulfide to form the 4-hydroxyoxazole (570) (73T1983). This normal C-acylation of the sulfonium ylide also leads to thiazoles with thiobenzoyl isocyanate in this case the initial acylation product was not isolated, the thiazole being obtained directly. 

Claisen ester condensation, 6, 279 Thiazolecarboxylic acid chlorides reactions, 6, 279-280 Thiazolecarboxylic acid hydrazides synthesis, 6, 280 Thiazolecarboxylic acids acidity, 6, 279 decarboxylation, 6, 279 reactions, S, 92 6, 274 Thiazole-2-carboxylic acids decarboxylation, S, 92 Thiazole-4-carboxylic acids stability, S, 92 Thiazole-5-carboxylic acids decarboxylation, S, 92 Thiazole-4,5-dicarboxylic acid, 2-amino-diethyl ester reduction, 6, 279 Thiazole-4,5-dicarboxylic acids diethyl ester saponification, 6, 279 Thiazolediones diazo coupling, 5, 59 Thiazoles, 6, 235-331 ab initio calculations, 6, 236 acidity, S, 49 acylation, 6, 256 alkylation, S, 58, 73 6, 253, 256 analytical uses, 6, 328 antifogging agents... 

Homologation ot aldehydes, ketones, acyl chlondes, two carbon homologation via 2-(tnmethylsilyl)thiazole... 

Aminomethyl)-4-(2-acyl-4-chlorophenyl)-l,3-thiazoles, e.g. 40a, b, prepared in situ by reduction of the 5-cyano derivative 39b, or by hydrolysis of the 5-phthalimido derivative 41a, cyclize in situ to the thiazolo[5,4-t/]-2-benzazepines, e.g. 41a, b.90... 

Aldehyde allgemeine ArbeitsvorschrifL Zu einer Suspension von 1 Mol 3-Oxo-2-acyl-2,3-dihydro-(ben-zo-[d]-l,2-thiazol)-l,l-dioxid in abs. Benzol wird unter Riihren und unter Stickstoff cine Losung von 0,5 Mol Natrium-bis-[2-methoxy-athoxy]-dihydrido-aluminat in abs. Benzol bei 0-5° innerhalb 5—10 Min. in kleinen Portionen gegeben. Man riihrt 2 Stdn. bei dieser Temp., vcrsetzt mit Wasser, saugt den Niederschlag ab, wascht mit Benzol nach, schiittelt die waBr. Phase mit Benzol aus, und dampft nach Trocknen die Benzol-Losungen ein. Der Riickstand wird destilliert bzw. kristallisiert. 

Diazadienes have been used in organic synthesis for the preparation of various heterocyclic compounds. Alkylation of 1,3-diazadienes 207 and the benz-fused analog 210 at the nitrogen atom by aryl acyl bromides provided the iV-alkyl amidinium bromides 208 and 211, which underwent annulation to the 2,3-dihydro-imidazo[2,l-A]thiazole 209 and imidazo[2,l- ]benzothiazoles 212, respectively (Equations 92 and 93) <2001S741, 2002J(P1)741>. 

Heterocyclic ring systems are also used to connect two anthraquinone groups. Typical examples include Cl Vat Red 10 (6.106), which is an oxazole derivative obtained from 2-amino-3-hydroxyanthraquinone and the appropriate acyl chloride, the similar thiazole derivative Cl Vat Blue 31 (6.107) and the oxadiazole derivative Cl Vat Blue 64 (6.108). 

The reaction of the biacetyl-trimethyl phosphite adduct (65) with acyl isocyanates has been extended to the isocyanates ROCONCO and PhCS-NCO.46 With the thiazolin-4,5-diones (66), (65) gave the thiazol-4-ones (67). 

Ochiai, who reported in 1936 the first synthesis of the imidazo[2,l-h]thia-zole system (36CB1650), transformed ethyl 2-mercapto-5-methyl-imidaz-oIe-4-carboxylate with monochloroacetone into 2-(acylalkylthio)-imidazole 36. Refluxing 36 in phosphorus oxychloride yields ethyl 3,5-dimethylim-idazo[2,l-h]thiazole-6-carboxylate. No cyclization could be achieved by heating 36 in acetic anhydride because N-acylation (to 37) inhibited further reaction to the bicyclic system. 

Russian authors investigated this important reaction type to prepare a wide range of aryl-, alkyl-, and acyl-substituted imidazo[2,l-ft]thiazoles (70KGS508, 70KGS512 71KGS389). Several 2-mercaptoimidazoles react with a-halo ketones in one step directly to the bicyclic products 35 under reflux in butanol or ethanol followed by basification. Yields vary between 52 and 99%, but the two-step cyclization route requires isolation of the intermediates 34 and subsequent heating in phosphorus oxychloride. 

The acylation of 5-hydroxymethylimidazo[2,l-h]thiazoles 96 (with, e.g., R = H, R = Ph) has been reported (80FES896). In line with expectations, ethyl esters of imidazol[2,l-6]thiazole carboxylic acids on basic hydrolysis... 

UV data for the parent compound are still lacking. Table V gives UV data for some 6-acyl substituted imidazo[2,l-h]thiazoles. 

Bromoacetylthianthrene, which can be produced by direct acylation as well as via bromination of 2-acetylthianthrene (63MI2) (for comparable dibromination of 2,7-diacetylthianthrene, see 64MI1), has been used in its capacity as an a-bromo-ketone to produce thianthren-2-yl-substituted heterocycles such as 55, 56, 57 (63MI2 73BSF1460), and 2-amino-4-(thianthren-2-yl)thiazole (63MI2), by condensation with 2-aminopyridine,... 

Acetazolamide Acetazolamide is 5-acetamido-l,3,4-thiadiazole-2-sulfonamide (9.7.5). The synthesis of acetazolamide is based on the production of 2-amino-5-mercapto-l,3, 4-thiadiazole (9.7.2), which is synthesized by the reaction of ammonium thiocyanate and hydrazine, forming hydrazino-N,N -( ji-(thiourea) (9.7.1), which cycles into thiazole (9.7.2) upon reaction with phosgene. Acylation of (9.7.2) with acetic anhydride gives 2-acetylamino-5-mercapto-l,3,4-thiadiazol (9.7.3). The obtained product is chlorinated to give 2-acetylamino-5-mercapto-l,3,4-thiadiazol-5-sulfonylchloride (9.7.4), which is transformed into acetazolamide upon reaction with ammonia (9.7.5) [24,25]. 

Nucleophilic attack at sulfur is implicated in many reactions of 1,2,4-thiadiazoles <84CHEC-I(6)463> and in general soft nucleophiles attack at sulfur. For example, reaction of 3-hydroxy-5-phenyl-1,2,4-thiadiazole (23) with acetic anhydride in the presence of dbu at 130°C gives the thiazoles (31) and (32) <85JHC1497>. These products may be reasonably explained by the mechanism outlined in Scheme 9 in which the thiadiazole ring is opened by the acetic anhydride carbanion. There is some evidence that (32) may arise from attack of the carbanion on the A-acylated derivative (30a) (Scheme 9) <85JHC1497>. 

A general synthetic route to meso-ionic iV-acyl-l,3-thiazol-5-imines (108, R = Ph, = Me, R = Me or Ph, R = COPh) is provided by treatment of thiobenzamidoaminoacetonitriles, Ph-CS-NMe-CHR-CN, first with benzoyl chloride and then with aqueous alkali. Alternatively, the thiobenzamidoaminoacetonitriles and hydrogen chloride give the corresponding salts, which with benzoyl chloride and aqueous alkali give -acyl l,3-thiazol-5-imines Derivatives (108, R = SMe) have been obtained by treating 5-acylamino-4-thiazoline-2-thiones with methyl iodide and aqueous alkali. ... 

Bicyclic derivatives (133) of l,3-thiazol-4-imines have been prepared by treatment of (2-pyridylthio)acetonitrile with acid chlorides. The same compounds (133) are also formed from 5-acyl-2-mercaptopyridine, chloroacetonitrile, and acid chlorides. 

Gyorgydeak et al. (69) converted a series of 2-substituted 3-acyl-l,3-thiazoli-dine-4-carboxylic acids (113) into the corresponding pyrrolo[l,2-c]thiazoles (115)... 

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