鈴木 教之

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.

The carbon-carbon bond formation reactions of diynes with EtMgBr can be catalyzed by Cp(2)ZrCl(2). The final products, magnesiated enynes, readily undergo stereoisomerization to give a mixture of (E) and (Z) isomers. The stoichiometric reaction of diynes with ethylene zirconocene gives zirconacyclopentenes with alkynyl substituents in the alpha position with high regioselectivities.

Treatment of alkynes with zirconocene-ethylene complex and homoallylic halides gave allylcyclopropane derivatives.

Reactions of zirconocene-alkyne complexes with allylic ethers afforded allylzirconation products of alkynes in high yields.

When ethylene and alkynes such as 4-octyne and diphenylacetylene were treated with CP2ZrBu2, highly pair selective coupling products were formed in high yields. Similarly, styrene or trimethylvinylsilane also afforded cross coupling products with alkynes on zirconocene complex.

Alcoholysis of zirconacyclopentenes proceeds at the alkyl carbon on Zr with high chemoselectivity in sharp contrast to monoiodination of Zirconacyclopentenes with iodine alcoholysis followed by iodination of Zirconacyclopentenes produces stereodefined trisubstituted alkenyl iodides in high yields with high isomeric purities.

（査読有）

Treatment of trans-3,4-diethylzirconacyclopentane complex, which was a selective butene-butene coupling product on zirconium, with methanol followed by bromine gave selectively monobromination product, 2-ethyl-3-methyl-1-bromopentane, in 89% yield with high stereoselectivity. Similarly, non-conjugated diene cyclization products on zirconium were also selectively converted into monohalogenated compounds. These selective monohalogenations proceeded via alkylalkoxyzirconocene complexes.

The reaction of monosubstituted alkenes with alkylmagnesium derivatives catalyzed by Cp2ZrCl2 or related zirconocene derivatives provides head-to-tail alkyl-alkene or alkene-alkene coupling products, approximately 50% of which are 2,5-dialkyl-4-pentenylmagnesium halides.

Reactions of zirconocene-alkene complexes with aldehydes gave alcohols as coupling products after hydrolysis. The carbon-carbon bond formation proceeded at C1 carbon of alkenes, in sharp contrast to the reactions of alkene-alkene coupling on zirconium. A similar alcohol was also obtained by the reaction of zirconacyclopentane with aldehyde after hydrolysis. Treatment of (C5Me5)2ZrEt2 with styrene gave 2-phenylbutane after hydrolysis contrary to the case of Cp2ZrEt2 which afforded 1-phenylbutane.

Hydrogenation reactions of alkenes were catalyzed by zirconium-alkene complex derivatives which are prepared from Cp2ZrCl2 (Cp = eta-5-C5H5) and n equiv. of RR'CHCH2M (M = MgX or Li). By the use of three or more equiv. of EtMgBr relative to Cp2ZrCl2, the product yield of hydrogenation of 1-decene was remarkably improved most likely due to the stabilization of the Zr(II) species.