Thiocarboxylates synthesis

Dewar and Turchi described the Comforth rearrangement of 5-alkoxyoxazole-4-thiocarboxylates as a potentially general method for the synthesis of 5-thiooxazole-4-carboxylic esters. Specifically, they found that thiol ester 13 underwent thermal isomerization to the corresponding 5-thiooxazole 14 in 94% yield. 

Because of the higher reaction rate, 7V(3)-alkylimidazolium-A ( 1 )-carboxylates or thiocarboxylates have often been used for the synthesis of carbamates and thiocarbamates by the azolide method instead of imidazole-iV-carboxylates. 

SYNTHESIS OF THIOLS, THIOETHERS, THIOACETALS AND S-ALKYL THIOCARBOXYLIC ESTERS... 

A procedure, which has been used successfully for the synthesis of dialkyl thioethers from thioacetamide has been extended to the preparation of a range of 5-alkyl thiocarboxylic esters [35] (Table 4.20). The intermediate 5-acyl ethaniminium salt (Scheme 4.14) is not stable and is converted directly into the 5-alkyl thioester. The choice of catalyst affects the yield of the thioesters. Thus, 5-n-octyl thiobenzoate... 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

The thiazole ring is assembled on the 5-carbon backbone of 1-deoxyxylulose 5-phosphate, which is also an intermediate in the alternative biosynthetic pathway for terpenes (Fig. 22-2) and in synthesis of vitamin B6 (Fig. 25-21). In E. coli the sulfur atom of the thiazole comes from cysteine and the nitrogen from tyrosine.374 The same is true for chloroplasts,375 whereas in yeast glycine appears to donate the nitrogen.372 The thiamin biosynthetic operon of E. coli contains six genes,372a 376 one of which (ThiS) encodes a protein that serves as a sulfur carrier from cysteine into the thiazole.374 The C-terminal glycine is converted into a thiocarboxylate ... 

The thiazole ring is synthesized from a pentulose or deoxypentulose 5-phosphate and either glycine or tryptophan, depending on the organism. Incorporation of sulfur leads to formation of hydroxymethyl thiazole, which is then phosphorylated. The sulfur comes from cysteine and is incorporated by formation of a thiocarboxylate at the carboxyl terminal of the enzyme, unlike biotin synthesis (Section 11.1.1), where an iron-sulfur cluster at the active site of the enzyme is the donor. 

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