Synthesis, metallation and nucleophilic reactivity of 2,6-bis(trialkylsilyl)-4H-thiopyrans

2,6-Bis(trialkylsilyl)-4H-thiopyrans constitute a new and interesting class of sulfur heterocycles. Their metallation converts them to a nucleophile which behaves most often like classically substituted 4H-thiopyrans. Thus, simple alkylation reactions proceed at positions 2 and 4 (mainly). On the other hand, in some cases the reaction follows a particular way, due to the stabilizing effect of silicon, as for the easy formation of thiabenzenes, or to its oxophilicity, as for the occurrence of Peterson process on addition to aldehydes. As expected, this effect is enhanced by the presence of a third silyl group in position 4. Whereas thiabenzenes are generally the result of addition of a nucleophile on a pyrilium salt, the 2,6-bis- and 2,4,6-tris(trialkylsilyl) substituted thiopyrans may be converted into thiabenzene via reaction of their lithium salt with electrophiles