Thiocarbonic esters

Nitro-aldols, which are readily available (see Henry reaction Section 3.1), are converted into olefins via conversion of the hydroxyl group to the corresponding phenyl thiocarbonate ester and treatment with tin radical.158 The yield was not reported. Because the radical deoxygenation via thiocarbonate (Barton reaction) proceeds in good yield, the elimination of Eq. 7.115 might be good choice for olefin synthesis.159... 

Thiocarbonate esters, obtained from aryl chlorothionoformates and hydroxyl groups, react similarly [206, 207]. This reaction was also used for the dehydration of oximes [208]. 

Both Bu3SnH and (Me3Si)3SiH are able to reduce alkyl iodides or bromides but not alcohols. However, in the Barton-McCombie reaction, they reduce certain alcohol derivatives, namely, ones that contain a C=S double bond (e. g., thiocarboxylic esters or thiocarbonic esters). Figure 1.39 shows how the OH group of cholesterol can he removed by means of a Barton-McCombie reaction. The C=S-containing alcohol derivative used there is a xanthate. 

For many years, the carbohydrate esters of carbonic acid and thiocar-bonic acid have found important application as intermediates in the synthesis of otherwise difficultly accessible derivatives. A review of these esters is particularly opportune, because both their preparation and properties are considerably influenced by stereochemical factors which require interpretation in the light of modem concepts of reaction mechanisms and conformational analysis. Although the historical development of the chemistry of the carbonic and thiocarbonic esters of carbohydrates has been independent, it is appropriate to give a comparative treatment of their closely related structures and properties. 

A need exists for a systematization of the nomenclature used for carbonate and thiocarbonate esters of carbohydrates, and the nomenclature employed in this review, based on modern chemical usage, shows clearly and unambiguously the nature of the groups described (see Table I). 

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

DiiNES et al. [16] have identified the products formed by inter-molecular rearrangement of thiocarbonate esters on heating. They were thus able to elucidate the mechanism of the reaction. They used loose layers of alumina (activity III according to Bbockmann) and chloroform-carbon tetrachloride-diethyl ether (30 + 30 + 40) as solvent. 

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