HIGHLY REGIOSELECTIVE REACTION OF ZIRCONOCENE-ALKENE COMPLEXES WITH ALDEHYDES OR KETONES

Reactions of zirconocene-alkene complexes Cp2Zr(CH2=CHRXPR3') (R = H, Me, Et, SiR3'' or Ar) with aldehydes or ketones were investigated. Zirconocene-ethylene, -propylene or 1-butene complexes reacted with aldehydes or ketones at terminal carbons of alkenes to give the corresponding alcohols after hydrolysis with a high regioselectivity. A similar type of reaction product was also obtained by a reaction of zirconacyclopentanes with aldehydes. This reaction proceeded via beta-beta' carbon-carbon bond cleavage of zirconacyclopentanes. A reaction of zirconocene-vinylsilane complexes with ketones afforded 3-trimethylsilyl-1-oxa-2-zirconacyclopentanes with an excellent regioselectivity. Carbon-carbon bond formation occurred exclusively at the terminal carbon of vinylsilanes. Their corresponding gamma-silylalcohols were obtained after hydrolysis. The products showed that vinylsilanes reacted with carbonyl compounds at the beta-carbon to silyl group. It is in sharp contrast to the conventional reactions of vinylsilanes of which the alpha-carbon normally attacked electrophiles. The reactions of styrene and its derivatives with pentan-3-one on zirconium gave a mixture of two regioisomers. Substituents of alkenes tend to be in alpha-position to Zr in 1-oxa-2-zirconacyclopentanes. This orientation showed a different aspect of the formation of 1-oxa-2-zirconacyclopentanes from the alkene-alkene coupling reaction on zirconium. The regioselectivity of the reaction with carbonyl compounds decreased in this order; R = alkyl > silyl > aryl.