Organosilane-Induced Synthesis and Functionalization of Sulfur-Containing Compounds

Abstract

Reactions of organothiosilanes with organic substrates generally lead to delivery of a sulfur moiety onto the target molecule, the precise outcome being related to the structure of the silyl sulfide used. Aromatic and aliphatic silyl sulfides react with carbonyl compounds under acidic or basic conditions to afford thioacetals and thioketals, but reactions with more activated compounds such as α,β-unsaturated acylsilanes give the Michael adducts, which represent versatile intermediates in organic synthesis. Silyl sulfides can also participate in substitution reactions of silyl enol ethers to afford vinyl sulfides. On the contrary, hexamethyldisilathiane reacts with various carbonyl compounds under the catalysis of CoCl2·6H2O or CF3SO3SiMe3 with thionation of the carbonyl unit, thereby providing a general access to thioketones and thioaldehydes, which can be trapped in situ by dienes. The use of CF3SO3SiMe3 in the reaction with cyclohexadiene gives rise to the interesting feature that stereopredetermined access to either the endo or the exo isomer can be obtained. Furthermore, when using aromatic or heteroaromatic o-azidoaldehydes, the reactivity of hexamethyldisilathiane may be finely tuned to drive the reaction towards the synthesis of o-azidothioaldehydes, fused isothiazole ring systems, or aromatic and heteroaromatic o-amino aldehydes and o-amino thioaldehydes. Lastly, by taking advantage of the high reactivity of the C−Si bond under fluoride ion catalysis, selective regiospecific thiophilic functionalizations of thioketones, dithioesters, trithiocarbonates, and their sulfines by various organosilanes such as allylsilanes, benzylsilane, and α-hetero-substituted silyl nucleophiles can be realized.