Recyclization reactions of heterocycles XVIII. Synthesis and recyclization of thiazolium and benzothiazolium salts

A number of thiazolium salts were obtained, and their reaction with hydrazine was studied. On reaction with hydrazine the aryl-substituted thiazolium salts are recyclized to dihydro-l, 2, 4-triazines, whereas on reaction with monoalkylhydrazines they are converted to 4H, 5H-1, 2-4-triazinium salts; thiazolium salts are converted to hydrazidohydrazones on reaction with phenylhydrazine. Recyclization to the dihydro-sym-tetrazine system was observed for 2-phenyl-substituted benzothiazolium tosylate.See [1] for communication XVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 635–640, May, 1976.     

Synthesis of new thiazolium betaines and the ring expansion reaction via 1,4-dipolar cycloaddition

The 1,4-dipolar cycloaddition of 3-phenyl-7-[N-pheny(carbamoyl)]-5,6-dihydroimidazo[2,1-b]thia-zolium betaine (7d) with a series of aliphatic alkylating agents such as ethyl bromoacetate, α-chloroacetone, and ethyl 4-chloroacetoacetate gave a variety of new ring-expanded cycloadducts 10a-c instead of ring transformation compounds 9 . This result was derived from the difference of reactivity between N- and S-alkylations of thiazolium betaines 7a,d. The advantage of our method is to prepare the triheterocyclic compounds 10a-c of complicated structure using reactive thiazolium betaine 7d in a one-pot without isolation of intermediates. Treatment of N-bridged thiazolo compounds 1a-c with benzoyl isothiocyanate led to new thiazolium betaines 2a-c , which were reacted with methyl iodide to afford the S-alkylated quarternary ammonium salts 3a-c. Synthesis of new 2-iminothiazolinium betaines 5a,b also was carried out.     

Acyloin condensation in aqueous system by durable polymer-supported thiazolium salt catalysts

We characterized three low-molecular-weight thiazolium salt analogues: N-methyl-5-(2′-benzyloxyethyl)-4-methylthiazolium iodide (MBMTI), N-methyl-4-phenylthiazolium iodide (MPTI), and N-methylbenzothiazolium iodide (MBTI). MBMTI, having high-electron density on the thiezolium ring, was found to be a durable thiazolium salt in buffer solution. Then, the polymer-supported thiazolium salt catalyst having MBMTI structure as a catalytic site for acyloin condensation was prepared by the polymerization of the corresponding thiazole monomer and the following quaternization. The polymer catalyst had excellent catalytic activity even in buffer solution, while the corresponding low molecular weight catalyst did not show any activity in aqueous system. Furthermore, the durable polymer catalyst could be reused under the aqueous condition. © 1994 John Wiley & Sons, Inc.     

Artificial enzymes with thiazolium and imidazolium coenzyme mimics

Hydrophobic thiazolium and imidazolium coenzyme mimics in the presence of modified-polyethylenimine enzyme mimics catalyze the benzoin condensation 2300-3300 times faster than the coenzyme mimics alone. Polycationic enzyme mimics provide not only a hydrophobic binding domain for coenzyme and substrate, but also electrostatic stabilization of anionic species that arise along the reaction pathway of the benzoin condensation.     

Coenzyme models. 32. Catalytic activity of polymer-bound thiazolium ions as estimated by flavin trapping technique

Three thiazolium-containing polymers, Th-7, Th-33, and Th-18-Py [where Th-x and Py mean x mol % thiazolium unit and pyridinium unit (54 mol %), respectively], were synthesized from partially p-chloromethylated polystyrene. The catalytic activities of these polymer catalysts in acyloin condensation of aldehydes and decarboxylation of α-keto acids were estimated kinetically by oxidative trapping of the key intermediate by flavin (flavin-trapping technique). In aqueous solution at 30°C, the catalytic activity of Th-18-Py and Th-33 in condensation of p-chlorobenzaldehyde was comparable with that of the cationic-micelle-bound thiazolium ion, whereas Th-7 and a monomeric thiazolium compound (N-benzylthiazolium bromide) scarcely exhibited any catalytic activity. The catalysis of the polymer-bound thiazolium ions was sensitively suppressed by increased ionic strength. These results suggest that the pendent thiazolium ion is activated by the relatively high charge density along the polymer chain: the cationic environment is able to facilitate dissociation of the thiazolium ion to the ylid form and deprotonation of the thiazolium-aldehyde adduct to the key intermediate.     

Facile oxidation of aldehydes and α-keto acids as catalyzed by flavin and thiazolium ion

Oxidation of aldehydes and α-keto acids to carboxylic acids ocurrs readily in the presence of a flavin, thiazolium ion, and cationic micelles, the reaction involving trapping by the flavin of the intermediate formed from the substrate-thiazolium adducts through deprotonation or decarboxylation.     

Facile synthesis of highly substituted 3-aminofurans from thiazolium salts, aldehydes, and dimethyl acetylenedicarboxylate

[reaction: see text] A facile preparation of 3-aminofuran derivatives via multicomponent reactions of thiazole carbenes, aldehydes, and dimethyl acetylenedicarboxylate (DMAD) is reported. In this process, the thiazole carbenes, generated in situ from thiazolium salts, reacted with aldehydes and DMAD at -78 to 0 degree C in CH(2)Cl(2) to afford the substituted furans in moderate to good yields. Eight substituted thiazolium salts were employed as carbene precursors in the reaction. Besides aryl aldehydes, alpha,beta-unsaturated aldehydes, aliphatic aldehydes, and arenedial were also investigated and found to be applicable to this reaction.     

Evidence for the involvement of a tetrahedral intermediate in H-D exchange of C-2 proton in thiazolium ion

Mechanism of H-D exchange of C-2 proton of thiazolium ion has been examined by PMR spectroscopy. Involvement of a tetrahedral intermediate, prerequisite to the exchage reaction, is proposed.     

Syntheses of new thiazolium salt polymers and their catalytic activities

Thiazolium salt polymers were synthesized for the purpose of obtaining a more efficient catalyst for the acyloin condensation. A new thiazolium salt, N-methyl-4-vinylphenylthiazolium iodide was synthesized. However, this compound did not homopolymerize by radical initiator. Therefore, 4-vinylphenylthiazole was polymerized and the obtained polythiazole was quarternized by methyl iodide. Poly(N-methyl-4-vinylphenylthiazolium iodide) was examined as a polymer-catalyst for the acyloin condensation of several aldehydes. This polythiazolium salt had an excellent catalytic activity in organic solvents, even in nonpolar solvents. Moreover, it was observed that the catalytic activity increases with the decrease of quarternization.     

An epoxide intermediate in nucleophilic acylations by thiazolium precursors

Computational work at the MP2/6-31+G(d,p) level is used to explore the nucleophilic species derived from the fluoride activation of O-silylated thiazolium carbinols. These species recently have been shown by Scheidt to be useful acyl anion synthons, but the mechanism of their formation has been an open question. The data point to an unusual spiroepoxide intermediate that rearranges via acid/base chemistry to give the active nucleophile. The addition of the nucleophile to nitroethene is also examined.     

Synthesis of 4-substituted 2-aminothiazoles and thiazolium salts derived from 2-chloroacetyl-1,3-cyclohexanediones

The reaction of 2-chloroacetyl-1,3-cyclohexanediones with thiourea and substituted thioureas forms 2-amino-4-(1,3-dioxo-2-cyclohexyl)thiazolium chlorides; in the presence of triethylamine 2-aminothiazole bases are formed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1409–1412, October, 1990.     

New aromatic systems having a fused thiazolium ring

The method developed for the synthesis of thiazolo[3,2-a]pyridinium salts has been extended to the first synthesis of simple thiazolo[3,2-a]pyrimidinium, thiazolo[3,2-a]-pyrazinium and thiazolo[2, 3-b]benzo[d]thiazolium salts. No method could be found for the cyclization of 4′-bromo-2-(2-benzoxazolylthio)acetophenone to the thiazolo[2,3-b]-benzoxazolium system.     

Imidazo[2,1-b]thiazolium salts based on 2-phenylamino-4-methylthiazole

Alkylation of 2-phenylamino-4-methylthiazole with substituted phenacyl bromides led to the synthesis of hydrobromides of 2-phenylimino-3-(p-R-phenacyl)-4-methylthiazoles. It was shown that, depending on the conditions of the cyclization of the last, 3-methyl-6-aryl-7-phenyl- or 3-methyl-5-aroyl-6-alkyl-7-phenylimidazo[2,1-b]thiazolium bromides can be synthesized. The spectral characteristics of the compounds synthesized were studied.Chernigov Technological Institute, Chernigov 250027. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 833–836, June, 1997.     

ROMPgel-supported thiazolium iodide: an efficient supported organic catalyst for parallel stetter reactions

[reaction: see text] A high-loading ROMPgel-supported thiazolium iodide was prepared via ROMPolymerization of the corresponding norbornene-derived monomer. The resulting ionic ROMPgel proved to be an efficient organic catalyst for Stetter reactions. The 1,4-dicarbonyl products, important intermediates in the synthesis of cyclopentenones and heterocycles, were obtained in high yields and excellent purities after minimal purification. The ROMPgel could be reused in up to four consecutive reaction cycles without significant loss of catalytic activity.     

The unprecedented ring transformation from thiazoline-spiro-thiophene to thieno[2,3-b]pyrazine involved in the reaction of 2-thiocarbamoyl thiazolium salts with dimethyl acetylenedicarboxylate

Reaction of 2-thiocarbamoyl thiazolium salts with dimethyl acetylenedicarboxylate proceeded via a tandem [3+2] cycloaddition and a unprecedented ring transformation to produce functionalized thieno[2,3-b]pyrazine derivatives in good to excellent yields.     

Design and synthesis of a bis(hydroxyphenyl)diamide bearing a pendant thiazolium unit; application to the catalytic asymmetric intramolecular Stetter reaction

The bis(hydroxyphenyl)diamide architecture constitutes as a privileged ligand that promotes a number of catalytic asymmetric transformations in combination with rare-earth metals. A new diamide analog armed with a carbene catalytic function derived from a thiazolium unit was designed, synthesized, and applied to the catalytic asymmetric intramolecular Stetter reaction. Cooperative work between the carbene function and hydrogen bonding interactions was suggested to give the enantioenriched chroman derivatives.     

Acyloin condensation by polymer supported thiazolium salt: Relation between the catalytic activity and the degree of quarternization

Thiazolium salt polymers were synthesized by the quarternization of thiazole polymers by alkyl halides. It was found that these polymers had high catalytic activities for the acyloin condensation of furfural. The catalytic activities of thiazolium salt polymers increased as the degree of quarternization decreased. This tendency was observed both in the polar solvents such as MeOH and in the nonpolar solvents such as dioxane. From the results of the acyloin condensation catalyzed by more hydrophobic polymer catalyst PTS⁺–St (which had styrene unit instead of free thiazole unit) and CnPTS⁺ (which had a long alkyl chain around the active site), it became clear that the hydrophobicity and the steric hindrance around the active site greatly affected the catalytic activity.     

胶团噻唑衍生物对安息香不对称合成反应的催化作用

通过α-(1-萘基)-N-硫代甲酰乙胺与卤代酮反应制得六个光学活性的4-烷基-3-α-(1-萘基)乙基噻唑溴化物烷基碳链长=1,2,7.11,15,21). 将其用于催化水溶液中的安息香缩合反应, 所得产物收率约20-30%具有较高的光学纯度(47-57%). 在各种缓冲溶液中测定了S(+)-4-甲基-3-α-(1-萘基)乙基噻唑氯化物(Ta)的胶团性质和由它催化的不对称安息香缩合反应. 临界胶团浓度(cmc)证明(Ta)在反应中确以胶团形式催化. 在硼砂溶液中, 安息香的收率高达61%, 光学纯度23.6%.     

Pyrrolo[2,1-b]thiazole derivatives by asymmetric 1,3-dipolar reactions of thiazolium azomethine ylides to activated vinyl sulfoxides

1,3-Dipolar reactions of thiazolium azomethine ylides to enantiopure cyclic and acyclic vinyl sulfoxides provide an efficient access to polyfunctionalized pyrrolo[2,1-b][1,3]thiazoles in a highly regio- and stereoselective manner. Regioselectivity can be inverted by modifying the position of the sulfinyl group at the double bond of the sulfinylfuranones. The sulfoxide is the main controller of the endo selectivity of these processes as well as of the pi-facial selectivity in reactions of (Z)-3-p-tolylsulfinylacrylonitriles. In contrast, the pi-facial selectivity in reactions of 5-alkoxy-3-p-tolylsulfinyl furan-2(5H)-ones is mainly controlled by the configuration at C-5, affording the anti adducts with respect to the alkoxy group as the major or exclusive adducts.     

Ring transformations of heterocyclic compounds. XVII, 2-(2,4,6-Triarylphenyl) substituted dihydro-1H-imidazolium,dihydrothiazolium and thiazolium salts from 2-methyl derivatives by pyrylium and thiopyrylium ring transformations

The synthesis of hitherto unknown 2-(2,4,6-triarylphenyl) substituted 4,5-dihydro-1H-imidazolium perchlorates 6 , 4,5-dihydrothiazolium perchlorates 8 and thiazolium perchlorates 9 from their 2-methyl derivatives 2 , 4 and 5 , respectively, by a 2,6-[C₅+C] ring transformation of 2,4,6-triarylpyrylium and -thiopyrylium salts 1/10 in ethanol in the presence of an appropriate base ( 6 : sodium ethanolate; 8,9 : anhydrous sodium acetate) is reported. Spectroscopic data of the transformation products and structural influences on their formation via anhydrobases of the salts 2 , 4 and 5 are discussed.