Thiocarbonylimidazolide

Imidazole-A-thionocarboxylates (also called thiocarbonylimidazolides ) are intermediates in a convenient radical-induced deoxygenation of primary and secondary alcohols with tributylstannane (Barton reaction).[1],[2]... 

A modification of the azolide method for deoxygenation of alcohols is the conversion of the thiocarbonylimidazolide with methanol into the thionocarbonate, which is then treated with tri-w-butyl stannane/AIBN. Thus, 2,3-dideoxynucleosides (a), (b), and a secodeoxynucleoside (c) have been prepared as follows [52H56]... 

Seven- and eight-membered oxygen heterocycles can be obtained starting from epoxycyclohexane thiocarbonylimidazolides and (C4H9)3SnH/AIBN.[663,[641... 

These include thiobenzoates, thiocarbonylimidazolides, and phenyl thionocarbonate esters.6 The S-methyl xanthate ester is a particularly convenient intermediate to prepare because of its ease of formation and the low cost of the reagents. Its use is precluded, however, by the presence of base-labile protecting groups and, in such cases, the thiocarbonylimidazolide or phenyl thionocarbonate ester will generally prove satisfactory. Additional methods for the radical deoxygenation of alcohols are described in a review by Hartwig.7... 

Radical chain chemistry is often employed for the transformation of an alcohol to the corresponding deoxy derivative. The secondary alcohol 1 is first converted into a suitable thiocarbonyl derivative. The first derivatives investigated were thioxobenzoates 2, xan-thates 3, and thiocarbonylimidazolides 4 (Scheme 2). On reduction with tributyltin hydride, these derivatives afforded a good yield of the appropriate deoxy compounds [8-10]. 

Deoxy-per-N-ethoxycarbonylseldomycin Factor 5 52 from the 3 -Thiocarbonylimidazolide 51 with TBTH [51]... 

A solution of per-N-ethoxycarbonylseldomycin factor 5-3 -thiocarbonylimidazolide 51 (Eq. (21)] (12.5 g, 12.58 mmol) in anhydrous dioxane (750 mL) was added dropwise to a refluxing suspension of tri-n-butylstannane (TBTH, 14.0 g, 12.7 mL, 48 mmol) in anhydrous dioxane (1200 mL) under a nitrogen atmosphere. After 2.5 h, the solvent was removed under reduced pressure, and the residue was chromatographed over silica gel to yield 9.8 g (90%) of 3 -deoxy-per-A -ethoxycarbonylseldomycin factor 5 52. 

Photolysis of PTOC imidate esters generated amidyl radicals which can undergo intramolecular homolytic substitution reactions (Scheme 29).152 The ratio of exo to endo products observed for the reaction of each of the thiocarbonylimidazolide diastereomers (70) and (71) with Bu3SnH was found to be different indicating that the intermediate radical (72) produced in each case was generated and reacted in a different conformation, respectively (Scheme 30).153... 

Wharton reaction (1, 439 8, 245). This reaction can also be conducted under free-radical conditions of reduction of thiocarbonylimidazolide derivatives of a,/l-epoxy alcohols with tri-n-butyltin hydride.17 In some cases, inverse addition is necessary to prevent further rearrangement of the allylic alcohol initially formed. Yields are around 50-60%. The modification is not useful in the carbohydrate field, where very complex product mixtures are formed. 

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