¹¹C-C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [¹¹C]methyl iodide

A novel ¹¹C-C bond formation based on the palladium-mediated cross-coupling reaction of alkenylzirconocenes with [¹¹C]methyl iodide is described. The conversion of internal alkynes into the corresponding alkenylzirconocenes followed by transmetalation with Pd(PPh₃)₄ and subsequent cross-coupling with [¹¹C]methyl iodide gave several ¹¹C-labelled alpha,alpha’-dimethyl substituted alkenes. The palladium complex Pd(PPh₃)₄ proved to be superior to Pt(PPh₃)₄ or Ni(PPh₃)₄ as transition metal complex.
The scope and limitations of the novel palladium-mediated cross-coupling reaction of alkenylzirconocenes with [¹¹C]methyl iodide were tested with various internal alkynes. Radiochemical yields of up to 75% (based upon [¹¹C]methyl iodide) could be achieved