Rapid methylation on carbon frame works for pet tracer synthesis: Part 7.: Rapid methylation on carbon frameworks useful for the synthesis of 11C H3-incorporated PET tracers:: Pd(0)-mediated rapid coupling of methyl iodide with an alkenyltributylstannane leading to a 1-methylalkenetl

The Pd(0)-mediated rapid coupling of methyl iodide with an excess of alkenyltributylstannane was examined with the aim of incorporating a short-lived C-11-labeled methyl group into a biologically significant organic compound with a 1-methylalkene unit for the synthesis of a PET tracer. Four sets of reaction conditions (A-D) were used, all performed in DMF at 60 degrees C for 5 min. Condition B, using CH3I/stannane/Pd-2(dba)(3)/P(o-tolyl)(3)/CuCl/K2CO3 (1 : 40 : 0.5 : 4-6: 2 : 5), works well in almost all cases. Condition D, using CH3I/stannane/Pd-2(dba)(3)/P(o-tolyl)(3)/CuX (X = Br, Cl, or I)/CsF (1 : 40 : 0.5-5 : 2-20 : 2-20 : 5-50), shows the best results with regard to general applicability to tin substrates, affording the corresponding methylated product in < 90% yield based on consumption of methyl iodide. P(t-BU)(2)Me was less effective than P(o-tolyl)(3), particularly for alpha,beta-unsaturated carbonyl substrates. No regio- or stereoisomerization occurred under these reaction conditions. The efficiency of the protocol was demonstrated by synthesis of an C-11-methylated compound.