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Richard J Whitby - One of the best experts on this subject based on the ideXlab platform.
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Tandem Insertion of Halocarbenoids and Lithium Acetylides into Zirconacycles: A Novel Rearrangement to Zirconium Alkenylidenates by β‐Addition to an Alkynyl Zirconocene.
ChemInform, 2011Co-Authors: Jozef Stec, Sally Dixon, Emma Thomas, Richard J WhitbyAbstract:Zirconocene complexes are used in the present one-pot three-component synthesis of carbocycles.
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Tandem Insertion of Halocarbenoids and Lithium Acetylides into Zirconacycles: A Novel Rearrangement to Zirconium Alkenylidenates by β‐Addition to an Alkynyl Zirconocene
Chemistry (Weinheim an der Bergstrasse Germany), 2011Co-Authors: Jozef Stec, Sally Dixon, Emma Thomas, Richard J WhitbyAbstract:Tandem insertion of 1,1-dihalo-1-lithio species (halocarbenoids) and lithium alkynides into zirconacyclopentenes and zirconcyclopentanes affords carbocyclic products in high yields via an unusual rearrangement which probably involves addition of an organolithium species to the ?-position of a zirconium-alkyne complex to give an alkenylidene-zirconate species. A wide variety of cyclopentanoid organic structures are rapidly assembled in good yield using this multi-component coupling. The main side reaction, which becomes exclusive in some cases, is ?-hydride elimination of an intermediate cyclopentyl- or cyclopentenyl-zirconocene.
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The regiochemistry of Zirconacycle elaboration
Tetrahedron, 2007Co-Authors: Emma Thomas, Sally Dixon, Richard J WhitbyAbstract:The regioselectivity of insertion of carbenoids into a variety of unsymmetrical zirconacyclopentanes is reported. For comparison the regioselectivities of isonitrile insertion and protonation have also been determined.
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Zirconium-Mediated Synthesis of Azepanes and Benzazepanes
Synlett, 2006Co-Authors: Donald P. S. Macfarlane, Richard J Whitby, David P. Norton, David Edward TupperAbstract:Intramolecular co-cyclisation of 4- or 5-azanona-1,8-dienes, -enynes and -diynes using zirconocene(1-butene) gives Zirconacycles which may be protonated to afford 3,4- or 4,5-disubstituted azepanes or, for the diyne derived systems, reacted with dimethyl acetylenedicarboxylate and CuCl to afford 2- or 3-benzazepanes.
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Zirconium mediated total synthesis of crinitol, 9-hydroxyfarnesoic acid, 9-hydroxyfarnesol, 9-hydroxysargaquinone and the selectively-protected aglycone of moritoside and euplexide A.
Chemical communications (Cambridge England), 2005Co-Authors: Sally Dixon, George J. Gordon, Richard J WhitbyAbstract:Tandem formation of an unsaturated Zirconacycle, insertion of methallyl carbenoid, and addition of an aldehyde provides a rapid synthetic route to several linear terpenoid and terpene–polyketide natural products.
Tamotsu Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Insertion Reaction of Aldehydes into Zirconacyclopentanes
Chinese Journal of Chemistry, 2010Co-Authors: Tamotsu TakahashiAbstract:Aldehydes reacted with zirconacyclopentane derivatives via insertion into the Zr-sp3C bond to afford the corresponding 7-membered Zirconacycles.
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Substituent effects in the preparation of naphthacenes by the coupling reaction of diyne-derived zirconacyclopentadienes with tetraiodobenzene.
Chemistry an Asian journal, 2008Co-Authors: Tomomi Seri, Lishan Zhou, Ken-ichiro Kanno, Tamotsu TakahashiAbstract:The synthesis of a series of substituted naphthacene derivatives through the coupling reaction of zirconacyclopentadienes with diiodobenzenes is reported. A reaction of bis(propargyl)benzenes with zirconacene dibutyl afforded the corresponding tricyclic zirconacyclopentadienes, which reacted with o-diiodobenzenes to afford the corresponding dihydronaphthacenes. The yields of the coupling reactions were dependent on the substituents on both of the Zirconacycles and o-diiodobenzenes. The reactions of diphenyl-substituted Zirconacycles gave higher yields than those of the alpha,alpha'-dialkyl-substituted derivatives. The iodide functions thus introduced allowed further introduction of substituents by well-established cross-coupling reactions after construction of the naphthacene skeletons.
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diallene formation by copper i mediated reactions of zirconacyclo pentanes with propargyl halides
Synthesis, 2005Co-Authors: Zheng Duan, Takahiro Nishimoto, Masamichi Ogasawara, Tamotsu TakahashiAbstract:In the presence of CuCl, zirconacyclopentanes reacted with two equivalents of a propargyl halide to give bisallenylation products in moderate to high yields. By controlling the amount of CuCl, stepwise allenylation was achieved and a variety of unsymmetrically substituted diallene derivatives were prepared as well.
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Haloamidation of alkynes and related reactions using Zirconacycles and isocyanates
Tetrahedron, 2004Co-Authors: Hiroshi Matsumura, Masamichi Yamanaka, Tamotsu TakahashiAbstract:Abstract Zirconacyclopentenes reacted with isocyanates to give aza- or oxaZirconacycles which were conveniently coverted into the corresponding haloamidation products of alkynes after halogenation. 1,4-Bistrimethylsilyl substituted zirconacyclopentadiene afforded a low yield of iodoamidation product, whereas zirconium–alkyne complexes stabilized with phosphine gave the iodoamidation products in moderate yields. On the other hand, zirconacyclopentanes reacted with isocyanates to give trimerization products of isocyanate, isocyanurates.
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Copper(I)-catalyzed tandem inter–intramolecular cyclization reactions of Zirconacycles: formation of highly substituted styrenes, vinylcyclohexadienes, and related compounds
Tetrahedron, 2002Co-Authors: Chisato Umeda, Martin Kotora, Hairong Guan, Tamotsu TakahashiAbstract:Abstract Copper(I)-catalyzed or mediated reactions of five-membered Zirconacycles with propargyl or allyl halides afforded a variety of useful vinylated cyclic compounds, including highly substituted styrenes, vinylcyclohexadienes and methylenecycloheptadienes, via tandem inter–intramolecular allylation reactions.
Miwako Mori - One of the best experts on this subject based on the ideXlab platform.
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Intramolecular Cyclization of Ene-Imine Using Dibutylzirconocene
Journal of Organic Chemistry, 2004Co-Authors: Muneyoshi Makabe, Yoshihiro Sato, Miwako MoriAbstract:The reaction of ene-imine with Cp2ZrBu2 was carried out. When a crude imine, which was prepared from ene-aldehyde and primary amine in the presence of MgSO4, was treated with Cp2ZrBu2 at room temperature overnight, cyclopentane derivative having trans-substituents was obtained in high yield along with a small amount of cyclopentane derivative having cis-substituents. Presumably, cis-Zirconacycle is a thermodynamic product. Reactions using various ene-imines were carried out. In the case of ene-imine prepared from ene-aldehyde and tBuNH2, only cyclopentane having cis-substituents was produced. In this reaction, chiral amine was used, and diastereoselective cyclization of ene-imine was carried out. As a result, cyclopentane derivative having cis-substituents was obtained in an optically active form after hydrogenolysis of the cyclized compound.
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Zirconium-Mediated Intramolecular Cyclization of Yne-Imine
Synthesis, 2004Co-Authors: Muneyoshi Makabe, Yoshihiro Sato, Miwako MoriAbstract:Successful zirconium-mediated intramolecular cyclization of yne-imine was achieved. When a crude imine, which was prepared from yne-aldehyde and primary amine in the presence of MgSO 4 , was treated with Cp 2 ZrBu 2 at roomtemperature for several hours, a cyclopentane derivative was obtained in high yield. The intermediary azaZirconacycle was treated with D 3 O + , I 2 or t-BuNC to give the desired deuterated, iodinated or formylated product, respectively, at the vinyl position in good yield. Transmetalation of Zirconacycle to CuCl was carried out and then allyl chloride was added to give an allylated compound in good yield. Selective bond fission of a zirconium-nitrogen bond of the azaZirconacycle was achieved by treatment of the azaZirconacycle with acyl halide to give an N-acylated vinylzirconium compound.
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Formation of Silazirconacyclopentenes from Zirconium−Silene Complex and Alkynes and Their Reactivities
Journal of the American Chemical Society, 2001Co-Authors: Shinji Kuroda, Yoshihiro Sato, Fumiko Dekura, Miwako MoriAbstract:During the course of our study on the formation of a complex having a zirconium−silicon bond, we found that zirconium−silene complex 7 was formed from Cp2ZrCl2 and Me2PhSiLi. In the presence of alkyne, diarylalkyne reacted with silene coordinated with zirconium to give silazirconacyclopentene 8. On the other hand, dialkylalkyne inserted into a zirconium−silene complex gave silazirconacyclopentene 9. Hydrolysis of 8 or 9 afforded vinylsilane 13 or allylsilane 16. Transmetalation of Zirconacycle 8 into copper in the presence of allyl halide gave a bis-allylated compound in high yield, indicating that alkylation occurred on the alkyne carbon and the methyl group of silicon. From bis-allylated compounds, eight-membered ring compounds having silicon were obtained in high yield using olefin metathesis.
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Novel Synthesis of Nitrogen Heterocycles Using Zirconium-Promoted Reductive Cyclization
The Journal of Organic Chemistry, 1994Co-Authors: Miwako Mori, N. Uesaka, Fumihiko Saitoh, Masakatsu ShibasakiAbstract:Perhydroindole derivatives were prepared from enynes using zirconium-promoted reductive cyclization. The Zirconacycles derived from enynes 1 were treated with iodine, isonitriles, oxygen, and carbon monoxide to give various heterocycles. The carbon-zirconium bonds of the Zirconacycle could be selectively cleaved by different reagents
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Novel Synthesis of Heterocycles Using Zirconium-Catalyzed Diene Cyclization
The Journal of Organic Chemistry, 1994Co-Authors: N. Uesaka, Miwako Mori, Kimio Okamura, Tadamasa DateAbstract:The catalytic cyclization of the diene 1 by Cp 2 ZrCl 2 in the presence of BuMgBr gives the hexahydroindole derivative 2. The stereochemistry of the Zirconacycle 10 is different from that of the Zirconacycle 7, which is obtained from 1 under stoichiometric conditions. Carbon-carbon bond formation results from treatment of the intermediary magnesium complex B with various electrophiles, such that various heterocycles were synthesized
Morris Srebnik - One of the best experts on this subject based on the ideXlab platform.
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Direct formation of cyclobutenylphosphonates from 1-alkynylphosphonates and Cp2ZrCl2/2EtMgCl/2CuCl
Tetrahedron Letters, 2009Co-Authors: Yulia Sinelnikove, Abraham Rubinstein, Morris Srebnik, Abed Al Aziz QuntarAbstract:Abstract Zirconacycles 2 prepared from 1-alkynylphosphonates 1 , zirconocene dichloride, and 2 equiv of EtMgCl are smoothly converted into cyclobutenylphosphonates 3 when treated with two equiv of CuCl in 65–81% isolated yield. The reaction is specific and general only for zirconacyclopentenyl phosphonates.
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Synthesis of 3-hydroxy-1-alkenylboronates via phosphine stabilized borylzirconacyclopropenes.
Chemical communications (Cambridge England), 2008Co-Authors: Abed Al Aziz Quntar, Alina Botvinik, Abraham Rubinstein, Morris SrebnikAbstract:Zirconacyclopropenylboronates can be stabilized to dimerization by complexation with tributylphosphine; the phosphine stabilized Zirconacycle boronates react with aliphatic and aromatic ketones and aldehydes at C2 of the triple bond to give the previously unknown 3-hydroxyvinylboronates in 61–80% isolated yields.
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Preparation of 5-hydroxy-1-alkenyboronates from 1-alkynylboronates, Cp2ZrCl2/2EtMgBr, and aldehydes.
Organic letters, 2004Co-Authors: Abed Al Aziz Quntar, Morris SrebnikAbstract:1-Alkynylboronates form five-membered Zirconacycles with Cp2ZrCl2/2-EtMgBr as indicated by deuterium labeling. The Zirconacycles add aldehydes to form seven-membered Zirconacycles. Hydrolysis of the latter provides 5-hydroxy-1-alkenylboronates in fair to good isolated yields. Both aliphatic and aromatic aldehydes undergo insertion.
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A study of the 1,2-addition of group IV metallacycles derived from 1-alkynylphosphonates to conjugated enones
Tetrahedron, 2004Co-Authors: Ofir Baum, Abed Al Aziz Quntar, Valery M. Dembitsky, Morris SrebnikAbstract:Addition of group IV cyclopropenemetallocycles to conjugated enones indicates that the reaction course is mostly dependent on the metallocyle and the enone moiety. The Zirconacycle affords the unrearranged products 3. On the other hand, some rearranged products, 1,3-butadienylphosphonates, are obtained when titanacycles are used.
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Highly Selective Preparation of 2-(Hydroxymethyl)vinylphosphonates by Insertion of Ketones into Zirconacycle Phosphonates
Synlett, 2002Co-Authors: Abed Al Aziz Quntar, Artem Melman, Morris SrebnikAbstract:Three-member Zirconacycles insert ketones exclusively at C-2 to give five-member Zirconacycle phosphonates that can be hydrolyzed to give 2-(hydroxymethyl)vinylphosphonates, 2, in excellent yields. Other regioisomers werenot detected. The reaction works well for both aromatic and aliphatic ketones. Competitive studies indicate that ketones and aldehydes insert at about the same rate and that both react much faster than alkynes. Compounds 2 undergo chlorination with thionyl chloride without rearrangement.
T. Don Tilley - One of the best experts on this subject based on the ideXlab platform.
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Mesityl Alkyne Substituents for Control of Regiochemistry and Reversibility in Zirconocene Couplings: New Synthetic Strategies for Unsymmetrical Zirconacyclopentadienes and Conjugated Polymers
Journal of the American Chemical Society, 2009Co-Authors: Adam D. Miller, Jennifer L. Mcbee, John F. Tannaci, Samuel A. Johnson, Hyuk Lee, T. Don TilleyAbstract:Reaction of 2 equivs of MesC≡CPh with Cp2Zr(η2-Me3SiC≡CSiMe3)(pyr) afforded the zirconacyclopentadiene Cp2Zr[2,5-Ph2-3,4-Mes2C4]. The regiochemistry of this isomer (ββ with respect to the mesityl substituents) was determined through single-crystal X-ray analysis and 2D (NOESY, HSQC, HMBC) NMR experiments. This selectivity is attributed largely to a steric-based directing effect of the o-methyl ring substituents since coupling of 1,3-dimethyl-2-(phenylethynyl)benzene with zirconocene gave a single regioisomer (o-xylyl groups in both β-positions) while coupling of 1,3-dimethyl-5-(phenylethynl)benzene gave a statistical distribution of zirconacyclopentadiene regioisomers. The coupling reaction of 2 equivs of MeC≡CMes or PrC≡CMes with Cp2Zr(η2-Me3SiC≡CSiMe3)(pyr) at ambient temperature gave the ββ regioisomers, Cp2Zr[2,5-Me2-3,4-Mes2C4] and Cp2Zr[2,5-Pr2-3,4-Mes2C4], respectively, as the major products. Heating solutions of these Zirconacycles at 80 °C for several hours resulted in an increase in the amount o...
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Mechanism of reversible alkyne coupling at zirconocene: ancillary ligand effects.
Journal of the American Chemical Society, 2008Co-Authors: Adam D. Miller, Jennifer L. Mcbee, T. Don TilleyAbstract:The mechanism of reversible alkyne coupling at zirconium was investigated by examination of the kinetics of zirconacyclopentadiene cleavage to produce free alkynes. The zirconacyclopentadiene rings studied possess trimethylsilyl substituents in the α-positions, and the ancillary Cp2, Me2C(η5-C5H4)2, and CpCp* (Cp* = η5-C5Me5) bis(cyclopentadienyl) ligand sets were employed. Fragmentation of the zirconacyclopentadiene ring in Cp2Zr[2,5-(Me3Si)2-3,4-Ph2C4] with PMe3, to produce Cp2Zr(η2-PhC⋮CSiMe3)(PMe3) and free PhC⋮CSiMe3, is first-order in initial Zirconacycle concentration and zero-order in incoming phosphine (kobs = 1.4(2) × 10-5 s-1 at 22 °C), and the activation parameters determined by an Eyring analysis (ΔH⧧ = 28(2) kcal mol-1 and ΔS⧧ = 14(4) eu) are consistent with a dissociative mechanism. The analogous reaction of the ansa-bridged complex Me2C(η5-C5H4)2Zr[2,5-(Me3Si)2-3,4-Ph2C4] is 100 times faster than that for the corresponding Cp2 complex, while the corresponding CpCp* complex reacts 20 times ...
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Reactions of Zirconacyclopentadienes with Nitrosobenzene. Characterization of Zirconacycle Intermediates and Formation of N-Phenylpyrroles
Organometallics, 2001Co-Authors: Masaaki Nakamoto, T. Don TilleyAbstract:Nitrosobenzene inserts into the Zr−C bond of zirconacyclopentadienes to give seven-membered zirconacyclic rings. The resulting insertion products are readily converted to N-phenylpyrroles and (in one case) a 3,3-spiroindole derivative.
