SELECTIVE CARBON-CARBON COUPLING WITH NUCLEOPHILIC THERMOLABILE METHYLCOBALT REAGENTS

Nonstabilized Co(II) methyl derivatives (MeCoCl, Me2Co, Me3CoLi, Me4CoLi2) are readily accessible in solution (THF, Et2O) by reaction of MeLi with CoCl2 at -78°C to -60°C. For checking the transmetallation process the "β-bromostyrene-ketone test" is especially favorable. Characteristic features of the reactivity of the Coreagents: High efficiency in the cross coupling with trans-β-bromostyrene, high aldehyde-vs.-ketone selectivity in Et2O, methylation of 2-cyclohexenone mainly in β-position, the ate-complexes methylate carboxylic esters, but not tertiary carbocyclic amides. © 1990.