Stereospecific Olefin Polymerization with Chiral Metallocene Catalysts

Current studies on novel, metallocenebased catalysts for the polymerization of α-olefins have far-reaching implications for the development of new materials as well as for the understanding of basic reaction mechanisms responsible for the growth of a polymer chain at a catalyst center and the control of its stereoregularity. In contrast to heterogeneous Ziegler–Natta catalysts, polymerization by a homogeneous, metallocene-based catalyst occurs principally at a single type of metal center with a defined coordination environment. This makes it possible to correlate metallocene structures with polymer properties such as molecular weight, stereochemical microstructure, crystallization behavior, and mechanical properties. Homogeneous catalyst systems now afford efficient control of regio- and stereoregularities, molecular weights and molecular weight distributions, and comonomer incorporation. By providing a means for the homo- and copolymerization of cyclic olefins, the cyclopolymerization of dienes, and access even to functionalized polyolefins, these catalysts greatly expand the range and versatility of technically feasible types of polyolefin materials. For corrigendum see DOI: 10.1002/anie.199513681     

应用芳基锂合成查尔酮

苯基锂、2-甲氧基苯基锂和2,4-二甲氧基苯基锂分别与肉桂酸反应以相当好的收率生成相应的查尔酮;2,6-二甲氧基苯基锂与肉桂酸不发生反应,但能与肉桂酸甲酯反应生成2',6'-二甲氧基查尔酮;类似的还制得了2',4',6'-三甲氧基查尔酮和2',4',4,6'-四甲氧基查尔酮.2,4-二甲氧基苯基锂和2,4,6-三甲氧基苯基锂也能与γ-丁酸内酯反应分别生成γ-羟丙基-(2,4-二甲氧基苯基)酮和γ-羟丙基-(2,4,6-三甲氧基苯基)酮.没发现三级醇生成.     

Synthesis of Orthogonally Protected S,S-2,6-Diaminopimelic Acid via Olefin Cross-Metathesis

A short synthesis of orthogonally protected S,S-diaminopimelic acid, DAP, via a selective cross-metathesis between S-allyl glycine and S-vinyl glycine followed by hydrogenation is reported. By analogy, the S,S-diaminosuberic acid, DAS, is produced by self-metathesis of S-allyl glycine, and the self-metathesis of S-vinyl glycine is described.     

Olefin isomerisation by group via metals

2-(MeR¹CCR²)-and 2-(CH₂CR¹CH₂CH₂)-pyridine (R¹,R² = H or Me) undergo 1,2-double-bond shifts and 2-(CH₂CHCH₂CH₂CH₂)-pyridine undergoes a 1,3-double-bond shift on displacement of norbornadiene from [M(CO)₄norb] (M = Cr, Mo or W) to give complexes of the type [M(CO)₄LL'] (LL' = 2-(allyl)or 2-(substituted allyl)-pyridine), which do not exhibit conformational isomerism involving the plane of the coordinated olefin.     

Synthesis of Dialkyl-substituted Terminal Olefin

Dialkyl-substituted terminal olefins were synthesized from the coupling reaction of a-olefins which were catalyzed by zirconocene dichloride/methylalumoxane （MAO） catalyst system under mild condition. High yield was gained and no other oligmer was detected. It was found that the ratio of AI/Zr is responsible for the selectivity of product.     

Synthesis of C‐Butenyl Linked Disaccharides via Olefin Cross‐Metathesis

Several C‐butenyl linked disaccharides were pre pared in high yields by olefin cross‐metathesis.     

Efficient and Stereospecific Synthesis of (z)-Hex-3-Enedioic Acid,a Key Intermediate for Gly-Gly cis Olefin Isostere

(z)-Hex-3-enedioic acid, a key intermediate in the synthesis of (z)-5-amino-3-pentenoic acid (a Gly-Gly cis olefin isostere), was synthesized by a short and efficient procedure of sequential oxidations. Thus, selective mono epoxidation of 1,4-cyclohexadiene was followed by periodate oxidation to the appropriate dialdehyde. Finally, Jones oxidation of the dialdehyde afforded the corresponding diacid product.     

Olefin copolymerization via reversible addition-fragmentation chain transfer

Successful statistical copolymerization of an alpha-olefin (1-octene) with an acrylate (butyl acrylate, BA) and with a methacrylate (methyl methacrylate, MMA), employing reversible addition-fragmentation chain transfer (RAFT) mediated polymerization has been accomplished     

立体脱氧合成环十六-9-烯内酯

以环十六-9,10-二羟基内酯为原料,经缩醛成环和立体脱氧合成环十六-9-烯内酯(2),其结构经1H NMR,13C NMR,IR和ESI-MS确证。抑菌活性和热性质研究结果表明:2在不同气氛中难以发生热裂解行为;2具有较好的抑菌作用,对白色念珠菌和宋内氏志贺氏菌的最小抑制浓度分别为992μM和62μM。     

Facile,Highly Stereoselective Synthesis of Cyclopropyl Benzoimidazoles via Cyclopropanation of Olefin with Arsonium Ylides

A facile and highly stereoselective methodology for the preparation of highly functionalized trans-1,2-cyclopropanes containing benzoimidazolyl, cyano, aryl, and carbonyl groups 3 is described. Arsonium bromides 2 reacted with electron-deficient olefins 1 in the presence of KF·2H₂O to provide 3 exclusively with high stereoselectivity in moderate to good yields.     

Stereospecific Synthesis of D-Glycero-D-ido-oct-2-ulose

Summary.  D-Glycero-D-gulo-heptose reacted with 2,2-dimethoxypropane to give its 2,3:6,7-di-O-isopropylidene derivative. Its base-catalyzed addition to formaldehyde resulted in the formation of 2,3:6,7-di-O-isopropylidene-2-C-(hydroxymethyl)-D-glycero-D-gulo-heptofuranose. After acid hydrolysis of this aldolization product, a new branched-chain aldose, 2-C-(hydroxymethyl)-D-glycero-D-gulo-heptose, was obtained, which was stereospecifically rearranged under the catalytic action of molybdic acid to D-glycero-D-ido-oct-2-ulose. Received October 17, 2000. Accepted December 4, 2000     

Stereospecific Synthesis of Methyl Vinyl Ketones

A stereospecific synthesis of enones 3 by coupling reaction of α-acetoxy alkyl methyl vinyl ketones 2 and Gilman or Grignard reagents in the presence of a catalytic amount of copper (I) salt at low temperature, is described.     

Random Block Copolymers via Segment Interchange Olefin Metathesis

Polycarbonate/polyethylene random block copolymers (RBCs) have been produced using olefin metathesis catalysis in a process termed segment interchange metathesis. An olefin metathesis catalyst tolerant of polar functionality was added to reagent polycarbonate and polyethylene polymers which contained internal unsaturated carbon–carbon bonds. Subsequent metathesis occurred, segmenting the reagent polymers, resulting in RBCs. The block copolymers self-assembled into microphase structures which persisted into the melt state as determined by small angle X-ray scattering (SAXS).

     

On the Synthesis of Chloro Derivatives of Five-Membered Heterocyclics via the Lithium Derivatives

In connection with our ¹³C NMR investigations we were interested in obtaining pure samples of 2- and 3-chlorofuran and 2- and 3-chloroselenophene. While direct chlorination with molecular chlorine or other chlorinating agents can successfully be used for the preparation of 2-chlorothiophene,¹ we could not reproduce either yields or isomeric purity in the corresponding chlorination of selenophene.^2,3