Reactions of geranyl and farnesyl halide, and their geometricalisomers with chlorotris(triphenylphosphine)cobalt(I) gave the corresponding geometrically pure coupling products under mild and non-basic conditions. Squalenes were stereospecifically synthesized by this method.
Allylicacetates were coupled with zinc dust in the presence of a catalytic amount of [Pd(PPh3)4] to give the corresponding 1,5-dienes under mild conditions in high yields. Significant co-solvent effects were found with methanol or 1,2-ethanediol in tetrahydrofuran.
The reaction of allylic acetates with zinc in the presence of a catalytic amount of hexacarbonylmolybdenum(0) led to reductive coupling for the formation of a 1,5-diene framework. Reductive coupling of nerolidyl acetate provided squalene and its isomers in high yield.