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

A novel 11 C–C bond formation based on the palladium‐mediated cross‐coupling reaction of alkenylzirconocenes with [ 11 C]methyl iodide is described. The conversion of internal alkynes into the corresponding alkenylzirconocenes followed by transmetalation with Pd(PPh 3 ) 4 and subsequent cross‐coupling with [ 11 C]methyl iodide gave several 11 C‐labelled α , α ′‐dimethyl‐substituted alkenes. The palladium complex Pd(PPh 3 ) 4 proved to be superior to Pt(PPh 3 ) 4 or Ni(PPh 3 ) 4 as transition metal complex. The scope and limitations of the novel palladium‐mediated cross‐coupling reaction of alkenylzirconocenes with [ 11 C]methyl iodide were tested with various internal alkynes. After heating at 60°C for 6 min radiochemical yields of up to 75% (based upon [ 11 C]methyl iodide) could be achieved. Copyright © 2006 John Wiley & Sons, Ltd.