4- , from 4-thiazole aldehyde

This procedure is representative of a new general method for the preparation of noncyclic acyloins by thiazol ium-catalyzed dimerization of aldehydes in the presence of weak bases (Table I). The advantages of this method over the classical reductive coupling of esters or the modern variation in which the intermediate enediolate is trapped by silylation, are the simplicity of the procedure, the inexpensive materials used, and the purity of the products obtained. For volatile aldehydes such as acetaldehyde and propionaldehyde the reaction Is conducted without solvent in a small, heated autoclave. With the exception of furoin the preparation of benzoins from aromatic aldehydes is best carried out with a different thiazolium catalyst bearing an N-methyl or N-ethyl substituent, instead of the N-benzyl group. Benzoins have usually been prepared by cyanide-catalyzed condensation of aromatic and heterocyclic aldehydes.Unsymnetrical acyloins may be obtained by thiazol1um-catalyzed cross-condensation of two different aldehydes. -1 The thiazolium ion-catalyzed cyclization of 1,5-dialdehydes to cyclic acyloins has been reported. 

This review collects a part of the results of work on the thiazole-aldehyde synthesis that has been carried out over several years by various individuals whose names are reported in the references. One of us (A.D.) would like to express to all of them his gratitude and appreciation for their contribution. Financial support came from the Progetto Finalizzato Chitnica Fine e Secondaria n. 2 (Rome), the Consiglio Nazionale delle Ricerche (CNR, Rome), the Ministero della University e della Ricerca Scientifica (MURST, Rome). One of us (A. M.) is grateful to the University of Ferrara for having been appointed as Lecturer in Organic Chemistry at the Faculty of Engineering. 

Thiazole-aldehyde synthesis Preparation of aldehydes from C-2 substituted thiazoles by thiazolyl-to-formyl conversion, see A. Dondoni, Carbohydrate synthesis via thiazoles, in Modem Synthetic Methods, R. Scheffold, ed., Verlag Helvetica Chimica Acta, Basel, 1992, p. 377 A. Dondoni, Acyclic diastereoselective synthesis using functionalized thiazoles. Routes to carbohydrates and related natural products, in New Aspects of Organic Chemistry, Z. Yoshida and Y. Ohshiro, eds., Kodansha, Tokyo, and VCH, Weinhcim, 1992, p. 105. 

Dondoni et al. prepared a 1-hydroxyethylene peptide using a thiazole-aldehyde synthesis starting from an amino acid.[38] The aldehyde is converted into an alkanoate by Wittig alkenation and reduction of the double bond (Scheme 18). Then, removal of the tert-bu-tyldimethylsilyl group gives the unsubstituted lactone. In the last step, the lactone is alkylated using the method reported by Kleinman and co-workers. 20 ... 

Hydroxy-4-hetarylthiazoles, from o-thio-cyanato-heteroarylketones, 273 2-HydtoxymethyM,5-dimethylthiazole, from 4,5-dimethylthiazole, 393 4-(Hydroxymethylthiazole), from 4-thiazole aldehyde, 341... 

A -Alkylated thiazolium salts are often used to introduce complexity into the thiazole heterocycle. The synthesis of imidazothiazole-chalcone derivatives as anti-cancer and apoptosis inducing agents by Kamal et al. at the Indian Institute of Chemical Technology illustrates this point. Here, a new class of imidaza[2,l-6]thiazole chalcone derivatives were synthesized from the corresponding imidazol[2,l-6]thiazole aldehydes, which in turn... 

Masked acyl anions feature as reactive intermediates in the dimerization of aldehydes to a-hydroxyketones catalyzed by thiazolium salts. Thiazole is a heteroaromatic compound (Section 25-4) containing sulfur and nitrogen. The salts are derived from thiazoles by alkylation at nitrogen and contain a resonance-stabilized positive charge (margin). 

The benzoin condensation has been examined computationally as a function of the structure of three carbene organocatalysts, that is, imidazol-2-, triazol-3-, and thiazol-2-ylidenes. DFT studies have featured three aldehydes and the historical mechanism of Breslow appeared to be consistent with the calculated reaction energy profiles whatever the aldehydexarbene combination was. It is noteworthy that the Breslow intermediate (118) arising from thiazol-2-ylidene proved to be much more stable than (119)/(120)... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

Most of the reduced thiazole derivatives were obtained from the reaction between l -Cys or its esters with aldehydes or ketones. L-Cystine reacts with formaldehyde at room temperature to give 4(f ) -thiazolidinecarboxylic acid 32 without racemization [36JBC(114)341 37JA200 78JMC1070]. 

Disubstituted imidazo[2,l-ft]thiazoles 41 have been prepared (55JCS1695 57JCS566) by eyelization of 1,5-disubstituted 2-mereaptoim-idazoles 40 in eonc. hydroehloric aeid. The latter eompounds were synthesized via eyelization of the thiourea derivatives 39. No aldehyde (42) was isolated from the reaetion obviously the thiourea eyelized more readily by reaetion with the aldehyde than with the keto group. 

Frank Burnett Dains, 1869-1948. Lecture assistant to Dr. W. O. Atwater at Wesleyan University, Middletown, Connecticut, and later assistant professor at Northwestern University and professor at Washburn College in Topeka, Kansas. From 1911 until tire time of bis retirement in 1942 he was in charge of the department of organic chemistry at the University of Kansas, where he made notable contributions to the chemistry of the aldehydes, urea ethers, substituted ureas, thiazoles, imidazoles, and pyrazoles, and was an enthusiastic collector of books, portraits, and other memorabilia connected with the history of chemistry. He was a charter member of the Chicago Section of the American Chemical Society and served as Councilor of the Society, as Chairman of the Divisions of Organic Chemistry and History of Chemistry, and as contributing editor and abstractor for the Journal of Chemical Education. See also ref. (166). 

Amino acids may also undergo thermal degradation, which is almost always coupled with some other food components, particular sugars. The major types of volatile compounds formed from amino-sugar interactions include Strecker degradation aldehydes, alkyl pyrazines, alkyl thiazolines and thiazoles and other heterocycles [35, 36]. As the subject has mainly relevance for baked and roasted vegetable food products, this subject will not be discussed in further detail. 

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