Highly Selective Synthesis of (<i>E</i>)-3-Methyl-1-trialkylsilyl-3-en-1-ynes via <i>trans</i>-Selective Alkynylation Catalyzed by Cl₂Pd(DPEphos) and Stereospecific Methylation with Methylzincs Catalyzed by Pd(<i>^t</i>Bu₃P)₂

Abstract

[reaction: see text] trans-Selective (>or=98%) monoalkynylation of 1,1-dibromo-1-alkenes and 1,1-dichloro-1-alkenes catalyzed by Cl(2)Pd(DPEphos) followed by stereospecific methylation with Me(2)Zn or MeZnX (X= Cl or Br) catalyzed by Pd((t)()Bu(3)P)(2) provides an efficient and stereoselective (>or=98%) route to 5, convertible to a wide variety of enynes and conjugated dienes. In the cases of 1,1-dibromo-1-alkenes, the Sonogashira alkynylation may also be satisfactory, but it is distinctly less satisfactory than the alkynylzinc reaction in cases where 1,1-dichloro-1-alkenes are used.