4-thiazolidinone ring system

Recently, an ultrasound-promoted synthesis of a series of medicinally relevant derivatives of the spiro[indole-thiazolidinone] ring system (compound 45) has been carried out from the three-component reaction of isatin, a 4-aminopyrazolin-3-one derivative and 2-mercaptopropionic acid in water, using cetyltrimethylammonium bromide (CTAB) as a phase-transfer catalyst (Scheme 1.20). This protocol avoided the need for either azeotropic removal of water or the use of a dehydrating agent, as required by conventional methods [28]. 

Fusion of s-triazole and 4-thiazolidinone rings can be effected in two possible ways, as exemplified by thiazolo[3,2-f ]-5-triazole-5(6//)-one (83) and thiazolo[2,3-c]-5-triazole-5(6//)-one (85). Only scanty work on these condensed thiazolidinone systems is available, although a considerable amount of work on their thiazole counterpart has been reported. 

The reaction of 247 with DMAD in methanol results in the exclusive formation of thiazinone 24. The reaction can be catalyzed by sodium methoxide. In the absence of added base, thiazolidinone 23 is formed in addition to compound 24. This is in contrast to the flndings in the reactions of thioureas with DMAD in which thiazolidinones are the only isolable products. The difference may be due to.the enhanced stability of the 6,5,6-ring system because of pseudoaromaticity and to the inherent strain present in the 6,5,5-ring system, or it may be due to the difference in basicity between a benzimidazolyl-2-thione and thioureas. 

The synthesis of naphthimidazo[2,l-fe]thiazol-3(2//)-ones, in which a 4-thiazolidinone nucleus has fused to both naphth[2,3-d]imidazole and naphth[l,2-c/]imidazole ring systems, has been reported. 

Imidazobenzothiazoles Synthesis and application 12JSC335. a/P-Mercaptoalkanoic acids Versatile synthons in the syntheses of fused ring 4-thiazolidinones/thiazolinones/thiazinanones ring systems 12JSC 439. 

Condensed heterocyclo[n,m-n, b, or cjquinazolines. 52, I Condensed 4-thiazolidinones, 49, I Condensed thiophene systems, tetra- and pentacyclic, 32, 127 Condensed 1,2,4-triazines I. Fused to heterocycles with three-, four-, and five-membered rings, 59, 39 Condensed l,2,4-triazolo[3,4-z) heterocycles, synthesis, 49, 277 Conformational equilibria in nitrogen-containing saturated six-membered rings, 36, I... 

Syntheses of different heterocyclic systems in which the 2,3- and 2,5-positions of 4-thiazolidinones (1) are attached to different rings have also come from Potts laboratory. 

The other three chapters in the present volume all deal with bicyclic heterocycles. Dr. H. K. Pujari of Kurukshetra University in India describes condensed 4-thiazolidinones, and Professor M. A. E. Shaban and A. Z. Nasr of Alexandria University in Egypt survey the synthesis of condensed 1,2,4-triazolo heterocycles. Finally, Professor T. A. Crabb of Portsmouth, England has covered saturated bicyclic 6/5 ring-fused systems with a bridgehead nitrogen and a single additional heteroatom. None of these groups of bicyclic heterocycles has been comprehensively reviewed before. 

Commercial hexythiazox is a racemic mixture of the two trans enantiomers Scheme 26.2.2 shows the main synthetic pathways [11, 17, 19]. Starting from 4-chloro propiophenone the key intermediate erythro amino alcohol may be obtained by stereoselective catalytic reduction of the corresponding hydroxy imi-noketone or by sodium borohydride reduction of the aminoketones obtained via Gabriel synthesis. Different routes lead from this aminoalcohol to the trans-thiazolidinone system the basis of all routes is activation of the hydroxy group, e.g., in form of the sulfonate and a ring forming reaction with carbon disulfide or carbonyl sulfide. The final acylation of the NH group with cyclohexyl isocyanate leads to hexythiazox. 

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