Ryuichiro Hara

Facile cleavage of the CβCβ′ bond of zirconacyclopentenes. Convenient method for selectively coupling alkynes with alkynes, nitriles, and aldehydes

Abstract The reaction of zirconacyclopentenes (1) with alkynes, nitriles, and aldehydes via cleavage of the CβCβ′ bond of 1 and displacement of ethylene by the donors to give the corresponding five-membered zirconacycles, providing a convenient means of selectively coupling alkynes with π-donor compounds.

Group 5 and group 6 metal halides as very efficient catalysts for acylative cleavage of ethers

Group 5 and 6 metal chlorides such as MoCl5, WCl6, NbCl5 and TaCl5 were found as very efficient catalysts for acylative cleavage of the C–O bond of ethers. Compared with conventional Lewis acid catalysts such as ZnCl2, AlCl3, SnCl4 and TiCl4, group 5 and 6 metal chlorides showed better results in the catalytic C–O bond cleavage of dibutyl ether with benzoyl chloride.

NOVEL TYPE OF CARBOZIRCONATION REACTION OF ALKYNES

Abstract Novel type of carbozirconation reaction of alkynes is reported. Treatment of zirconocenealkyne complexes, zirconacyclopentenes, or zirconacyclopentadienes with allylic compounds gave allylzirconation products of alkynes. Carbozirconation of alkynes with zirconacyclopentenes or zirconacyclopentadienes involved β,β′-C-C bond cleavage reaction of zirconacycles. Reactions of zirconacyclopentenes with homoallyl bromides afforded allylcyclopropane derivatives as carbozirconation products.

Allylzirconation of alkynes by the reactions of zirconocene-alkyne complexes with allylic ethers

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

Highly substituted enyne formation by coupling reaction of alkenylzirconium compounds with alkynyl halides

Abstract Alkenylzirconium compounds, which were prepared by carbozirconation or hydrozirconation of alkynes, reacted with alkynyl halides in the presence of CuCl to give highly substituted 1,3-enynes in good yields. This reaction was done conveniently in one-pot from alkynes.

Chemoselective functionalization of zirconacyclopentenes

Abstract Zirconacyclopentenes, which were readily prepared by the reaction of Cp 2 ZrEt 2 with alkynes or by the reaction of vinylsilane with alkynes in the presence of Cp 2 ZrBu 2 (Negishi reagent), reacted with iodine to give either stereodefined alkenyl iodides or homoallylic iodides selectively after hydrolysis. The chemoselectivity of this reaction was strongly dependent on the substituent R group of the C2 carbon attached to zirconium. When R was a phenyl group, homoallylic iodides were selectively formed. On the other hand, alkyl substituted zircona- cyclopentenes reacted with iodine to afford alkenyl iodides selectively. A small amount of diiodides were produced as by-products. Reactions of zirconacyclopentenes with an excess of MeOH and iodine in this order gave only alkenyl iodides with excellent selectivities. The formation of diiodides was not detected. This monohalogenation procedure using an excess of MeOH/I 2 was not substituent dependent in the system used here. Treatment of alkylsubstituted zirconacyclopentenes with CBr 4 or CCl 3 Br yielded only homoallylic bromides, after hydrolysis, with > 99% chemoselectivity. It is in sharp contrast to the reaction with usual bromination reagents such as Br 2 and NBS which led to the selective formation of alkenyl bromides. A sequential treatment of zirconacyclopentenes with CBr 4 and I 2 in this order, afforded a mixed dihalogenation product selectively. Reaction with Me 3 SnCl was not substituent dependent. The sp 3 carbon attached to Zr selectively reacted with Me 3 SnCl to give homoallyltin compounds. Insertion reaction of isonitrile in the Zr-carbon bond of zirconacyclopentenes were chemoselective but neither substituent dependent nor reagent dependent in the system used here.

Highly selective monofunctionalization of zirconacyclopentanes and dialkylzirconocene complexes

Abstract Selective monofunctionalization was investigated for symmetrical zirconacyclopentanes or symmetrical dialkylzirconocenes. Reaction of zirconacyclopentanes, which were prepared by intermolecular coupling of two alkenes, or intramolecular cyclization of dienes, trienes or tetraenes on zirconium, with PPh2Cl or SnR3Cl (R = Me, Ph) gave monofunctionalized products in good to high yields with high selectivities. Even in the presence of 2 equiv. of PPh2Cl or SnR3Cl, only one Zr-carbon bond reacted. Treatment of zirconacyclopentanes with methanol yielded monoprotonated complexes. Subsequent addition of halogen such as Br2 and I2 to these monoprotonated complexes gave highly selective monohalogenated products. Similar monoprotonation reactions proceeded for dialkylzirconocene or-hafnocene complexes. Reaction of Cp2MR2 (M = Zr or Hf, R = alkyl or aryl) with alcohols afforded alkylalkoxyzirconocene or -hafnocene complexes, Cp2MR(OR′) (M = Zr or Hf, R′ = alkyl or aryl) in high yields with high selectivities. High selectivity of monofunctionalizetion using PPh2Cl, SnR3Cl or alcohols can be attributed to the different reactivities between monoalkylzirconocenes which are monofunctionalized products and zirconacylclopentanes or dialkylzirconocenes.

Allene formation by coupling of propargylic ethers with olefins via β-alkoxide elimination of zirconacycle intermediates

Abstract A zirconoceneethylene complex reacted with propargylic ethers to give allene derivatives in good yields via β-alkoxide elimination. Deuterolysis of the reaction mixture revealed that the final product after elimination still had a zirconiumcarbon bond. Coupling of styrene and propargylic ethers was mediated by Cp 2 ZrBu 2 (Negishi reagent) to give phenethyl allene derivatives. β-Alkoxide elimination from zirconacyclopentadienes bearing two α-CH 2 OMe groups was also observed. One CH 2 OMe group was easily eliminated. Elimination of the second CH 2 OMe group was dependent on its structure.

CATALYTIC DECHLORINATION OF AROMATIC CHLORIDES USING GRIGNARD REAGENTS IN THE PRESENCE OF (C5H5)2TICL2

Dechlorination of aromatic chlorides was efficiently performed with alkyl Grignard reagents in the presence of a catalytic amount of (C5H5)2TiCl2.

Allene formation by the reaction of olefins with propargyl silyl ethers mediated by a zirconocene complex

Abstract Ethylene and styrene derivatives reacted with various propargylic ethers in the presence of zirconocene(II) to afford allenic products in high yields. The reaction proceeded via formation of zirconacyclopentenes by selective coupling of an olefin and a propargylic ether, which was followed by β-elimination of the siloxy group. Deuterolysis confirmed that the final product had a zirconium-carbon bond.