Reaction of Tantalum-Alkyne Complexes with Isocyanates or Acyl Cyanides. Stereoselective Functionalization of Carbon-Carbon Triple Bonds

Article abstract of DOI:10.1246/bcsj.65.1543

Treatment of alkynes with low-valent tantalum derived from TaCl5 and zinc produces tantalum-alkyne complexes (not isolated), which react in situ with phenyl isocyanate (or butyl isocyanate) to give (E)-α,β-unsaturated amides stereoselectively.The tantalum-alkyne complexes also react with acyl cyanides in the presence of BF3*OEt2 to give α-cyanohydrins.In both reactions, filtration of the reaction mixture containing the tantalum-alkyne complexes before addition of isocyanates (or acyl cyanides) is indispensable to obtain good yields.