Thionocarbonic acid ester

Replacement of hydroxyl groups by hydrogen via thionocarbonic acid esters... 

Sulfinic acid alkoxymethyl esters Thionocarbonic acid esters Thiocarbonate esters 40... 

Cyclic thionocarbonic acid esters from disulfurdicarbothionates by rearrangement fragmentation... 

Sodium hydroxide/H2O2 (Hydroxythiol)thionocarbonic acid esters of carbohydrates... 

Sodium/alcohol Thionocarbonic acid esters from xanthates... 

Carbonic acid (67) can form three different types of thio derivatives, namely thionocarbonates (68), dithiocarbonates (69) and trithiocarbonates (70) (Figure 4). Only the trithioacid (70) is known to exist as the free acid, although all the acids can be isolated as their salts and esters. The mono-, di-and trithioesters (71-(73) can be prepared by the reaction of thiophosgene with alkoxides, phenolates and thiols, respectively (Scheme 38). 

Of the two enantiomeric malic acid methyl esters, the 7 -isomer 539 is considered less accessible and considerably more costly. Several attempts at its synthesis have been made [170,171,172], but a very expedient two-step synthesis from dimethyl (+ )-(i ,i )-tartrate (la) provides (i )-dimethylmalate (539) in 67% yield. Treatment of lb with thiocarbonyldiimidazole affords in 76% yield the thionocarbonate 538 which, when treated with tri-n-butyltin hydride furnishes, after facile chromatographic purification, multigram quantities of pure 539 [173]. 

The use of unsymmetrical sulphites in glycoside synthesis is mentioned in Chapter 3. Reduction of dimethylsulphamoyl esters to deoxy compounds is noted in Chapter 11. Reference to ascorbic acid sulphates and phosphates is made in Chapter 15. Phenylboronates used for disaccharide synthesis are mentioned in Chapter 3. Chapter 4 includes a mention of an alkene synthesis via a thionocarbonate. 

Radical Coupling and Cyclization Reactions. Phenyl thionocarbonate esters derived from alcohols serve as efficient precursors for the generation of radical intermediates which can be used for the formation of new carbon-carbon bonds. For example, a 4-thionocarbonate ester derived from L-lyxose undergoes a stereoselective allylation upon photolysis in toluene in the presence of 2.0equiv ofAllyltributylstannane (eq 6). Photoehemical initiation is preferable to chemical initiation using Azobisisobu-tyronitrile which results in the formation of side products at the expense of the desired product. The allylation produet was used further in a total synthesis of pseudomic acid C. 

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