Thionocarbonic esters

Silylated 1,4-cyclohexadienes were introduced as reducing agents in radical chain reactions such as dehalogenation, deoxygenation via thionocarbonate ester and deselenization [120]. Two examples are given in Reactions (4.75)... 

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... 

The tributyltin hydride reduction usually proceeds without complications. The most common byproduct is starting alcohol, which is postulated to be derived from a mixed thioacetal. Use of the phenyl thionocarbonate ester has been reported to minimize this side reaction in cases where it is a problem.6... 

Table 2. Barton-McCombie deoxygenation of phenyl thionocarbonate esters comparison of the catalytic with the stoichiometric reaction [25].

It is a useful reagent for deoxygenating phosphine oxides to phosphines, and will redueed chiral phosphine oxides to chiral phosphines with retention of eonfiguration [Marsi J Org Chem 39 265 1974]. It is a reducing agent in radical reactions [Perez et al. J Org Chem 52 5570 1967], and deoxygenates primary and seeondaty alcohols via their xanthate or thionocarbonate esters (prepared from aryl-OCSCl and an inhibitor, e.g benzoyl peroxide) in 60-100 minutes in >87% yields [Barton et al. Synlett 435 7997]. [Beilstein 16 III 1198,16 IV 1360.]... 

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 2.0 equiv of allyltributylstannane (eq 6). Photochemical initiation is preferable to chemical initiation using azobisisobu-tyronitrile which results in the formation of side products at the... 

Oxime ethers derived from hydroxy aldehydes, upon conversion to their phenyl thionocarbonate esters, undergo radical cyclizations resulting in the formation of carbocycles. For example, an oxime ether obtained from D-glucose is converted into its phenyl thionocarbonate ester at C-5 and, upon heating in benzene in the presence of tributyltin hydride, affords cyclopentanes in 93% yield as a 62 38 mixture of two diastereomers (eq 7). In general, only low to modest stereoselectivity between the newly formed stereocenters is observed in a number of substrates examined. 

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