Radicals from thiono esters

Radicals formed by fragmentation of xanthate and related thiono esters can also be trapped by reactive alkenes.217 The mechanism of radical generation from thiono esters was discussed in connection with the Barton deoxygenation method in Section 5.4. 

Equation (24) has been chosen as an example of the radical deoxygenation of secondary alcohols via thiono esters [58], whereas Eq. (25) represents an example of deamination of primary amines via isocyanides [7, 54]. The reaction mechanism of these reductions is similar to that described for tin hydride, i.e. attack of silyl radical on the C=S or N=C moieties to form a radical intermediate which undergoes -scission to form alkyl radicals. Hydrogen abstraction from the hydride gives the product and the (TMS)3Si radical, thus completing the cycle of this chain reaction. 

Deoxygenation of primary and secondary alcohols.1 This deoxygenation has been effected by reduction of the thiocarbonyl esters with tributyltin hydride and AIBN as the radial initiator (11, 550). A newer, milder method uses diphenylsilane in a radical chain reaction initiated by triethylborane and air. Even secondary thiono-carbonates, particularly those derived from 4-fluorophenol, are deoxygenated at 25°. 

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