The highly α,α′ selective and stereocontrolled homocoupling reaction of allylic halides was achieved using barium reagent. The double-bond geometry of the starting allylic chloride was completely retained. The α,α′ cross-coupling products were also prepared stereospecifically and regioselectively by this method.
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.