Sulfides, alkynyl silyl

In the presence of a catalytic amount of Sc(OTf)3, imines and alkynyl sulfides undergo [2 + 2] cycloaddition and successive fragmentation to afford a, -unsaturated thioimidates (eq 21)/ Alkynyl selenides or alkynyl silyl ethers undergo similar reactions in the presence of Sc(OTf)3. 

Nucleophilic reactions of lithium thioalkynolates with electrophiles mostly occur at the 3 -position to afford alkynyl sulfides. For example, 3 -silylation and 3 -stannation are shown in equation 80 the synthesis and -alkylation of a quaternary ammonium thioalkynolate are shown in equation 81. Exceptionally, lithium thioalkynolates add to ketones to form -thiolactones, which are converted into alkenes on elimination of carbon oxysulfide (equation 82). Contrary to lithium ynolates, thioalkynolates do not react with aldehydes. ... 

---