SILICON-ASSISTED SYNTHESIS OF THIOCARBONYL DERIVATIVES AND REACTIVITY OF DIENOPHILIC THIOALDEHYDES

Treatment of bis(trimethylsilyl) sulfide with CoCl2.6H2O in the presence of aldehydes affords the corresponding thiocarbonyl analogues which can be trapped to avoid polymerization. The sulfurization reaction also takes place in the presence of TfOSiMe3, in which case, besides thioaldehydes, thioketones may be obtained in satisfactory yields. When thioaldehydes are generated with the CoCl2.6H2O method the Diels-Alder reaction with cyclohexadiene occurs with very high selectivity in favor of the endo isomer, whereas when the TfOSiMe3-based method is employed, the stereochemistry of the cycloadduct can be conveniently selected toward endo or exo by varying the molar ratio of the sulfurating agent.