Reduction thiazolidine derivative

In the next example, the strategy for the formation of fused cyclic ethers utilized the formation of an intermediate a-heterosubstituted carbon radical, generated by the reaction of (TMS)3Si radical with A-(ethoxycarbonyl)-l, 3-thiazolidine derivative [38]. This intermediate gives intramolecular C — C bond formation in the presence of proximate 1,2-disubstituted double bonds (Reaction 7.27). However, when terminal double bonds are used, the hydrosily-lation of the double bond by (TMS)3SiH can compete with the reduction and prevent forming the desired C—C bond formation. 

Peptide aldehydes can be synthesized via hydrolysis of thiazolidine precursors with mercury or copper salts (Scheme 10). 56 The Phe-thiazolidine derivative 27 was prepared from reduction of dihydrothiazole ring in 26, which was formed from a (5-hydroxy thioamide cyclization of 25 using the Mitsunobu reaction. N-Terminal Boc and Z groups on thiazolidine pseudopeptides such as Boc-Ala-Phe-thiazolidine and Z-Phe-Tyr-thiazolidine are stable to hydrolysis that affords Boc-Ala-Phe-H and Z-Phe-Tyr-H. 56 ... 

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

Reduction of dihyro compounds to the tetrahydro derivatives is sometimes possible. For example, thiazolines are reduced to thiazolidines by aluminum amalgam. 

Examples of this ring system (263) were prepared by cyclocondensation of anthranilic acid with the 1,3-thiazole derivatives 262 (82MI1 83AP394). Reductive cyclization of the 4-ethylamino-3-(2-nitrobenzyl)thiazolidines (264) was affected by heating with iron filings and acetic acid to give 4//-3,3a-dihydrothiazolo[4,3- >]quinazoline (265) (87JHC107). 

Cleavage of a thiazolidine ring is observed151 in the reduction of the condensation product between cysteine and pyridoxal, 2-(2-methyl - 3 - hydroxy - 5 - hydroxymethyl - 4 - pyridyl)thiazolidine - 4 -carboxylic acid (131). The reduction is best understood when the compound is considered as a derivative of 4-pyridine carbaldehyde... 

A relatively simple derivative of phenylalanine shows hypoglycemic activity. This compound, nateglinide, is usually prescribed for use as an adjunct to either metformin, or one of the thiazolidine hypoglycemic agents. Catalytic reduction of the benzoic acid (85) leads to the corresponding substituted cyclohexane as a mixture of isomers. This compound is then esterified with methanol to give the methyl esters (86). Treatment with sodium hydride leads 86 to equilibrate to the more stable trans isomer 87 via its enolate. Condensation of 87 with the ester of phenylalanine (88) yields nateglinide (89) after saponifications. ... 

Acyl-1,3-thiazolidines-2-ones 1.123 (X = S, R = COOMe), obtained from cysteine methyl ether [261], have been introduced by Mukaiyama and coworkers for use in asymmetric aldol reactions [261, 433, 434, 435], In reactions of related //-acyl-1,3-oxazolidines-2-thiones 1.123 (X = O, R = COOMe), each enantiomer can be obtained either from L- or D-serine [434] and the auxiliaries can easily be recovered by methanolysis. Similarly, //-acyl derivatives of 1.121 (X = S) have been used in asymmetric aldol reactions [429, 436], and //-acyl- 1,3-thiazo-lidinethiones 1.123 (X = S, R = r -Pr) are useful in asymmetric acylation [437] and aldol and related reactions [437, 438], Cleavage of the chiral auxiliary is accomplished by aminolysis with O-benzylhydroxylamine or by reduction with LiAlH.,. ... 

Carbonyl Group Reduction. The flow of new methods for reduction of acid derivatives and aldehydes or ketones to alcohols continues unabated. The Report last year (4,134) featured the sodium borohydride reduction of carboxylic acid derivatives, originally thought to be 2-thiazoline-2-thiol esters (14), to give alcohols in good yields. Full details of the method have now appeared (Scheme 8), and it seems that the acid derivatives are in fact the 3-acyl thiazolidine-2-thiones (IS) dissappearance of their yellow colour is an easy way to monitor the reduction. Carboxylic acids or their chlorides can also be reduced to primary alcohols in good yields at room temperature using a titanium tetrachloride-sodium borohydride combination. ... 

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