New Methods for the Preparation of Multiply Substituted Cyclopentadienes and Related Compounds

Substituents on cyclopentadienyl ligands significantly influence the reactivity and catalytic efficiency of their transition metal complexes. Therefore, development of synthetic methods for cyclopentadiene derivatives possessing different substituents has been in great demand. In this paper, we report new synthetic methods for multiply substituted cyclopentadienes recently developed in this group. In principle, three types of preparative methods are described. Firstly, zirconacyclopentadienes in the presence of Lewis acids react with aldehydes to afford multiply substituted cyclopentadienes, thus providing a one-pot procedure from two molecules of identical or different alkynes and one molecule of aldehyde; reaction of aluminacyclopentadienes with aldehydes also result in high-yield formation of multiply substituted cyclopentadienes. Secondly, 1,2,3,4-tetrasubstituted 1,4-dilithio- and 1,4-bis(magnesiobromo)-1,3-diene derivatives react with aldehydes or ketones via deoxygenation of the C=O moieties to afford cyclopentadiene derivatives. Thirdly, monolithio reagents, 1,2,3,4-tetrasubstituted 1-lithio-1,3-butadienes, and Grignard reagents, 1,2,3,4-tetrasubstituted 1-magnesiobromo-1,3-butadienes react with aldehydes or ketones to afford cyclopentadiene derivatives upon hydrolysis.     

Cross-coupling reaction of alkyl halides with grignard reagents catalyzed by Ni, Pd, or Cu complexes with pi-carbon ligand(s)

Transition metal-catalyzed cross-coupling reactions of organic halides and pseudo-halides containing a C-X bond (X = I, Br, Cl, OTf, OTs, etc.) with organometallic reagents are among the most important transformations for carbon-carbon bond formation between a variety of sp, sp(2), and sp(3)-hybridized carbon atoms. In particular, researchers have widely employed Ni- and Pd-catalyzed cross-coupling to synthesize complex organic structures from readily available components. The catalytic cycle of this process comprises oxidative addition, transmetalation, and reductive elimination steps. In these reactions, various organometallic reagents could bear a variety of R groups (alkyl, vinyl, aryl, or allyl), but the coupling partner has been primarily limited to sp and sp(2) carbon compounds: alkynes, alkenes, and arenes. With alkyl coupling partners, these reactions typically run into two problems within the catalytic cycle. First, oxidative addition of alkyl halides to a metal catalyst is generally less efficient than that of aryl or alkenyl compounds. Second, the alkylmetal intermediates formed tend to undergo intramolecular beta-hydrogen elimination. In this Account, we describe our efforts to overcome these problems for Ni and Pd chemistry. We have developed new catalytic systems that do not involve M(0) species but proceed via an anionic complex as the key intermediate. For example, we developed a unique cross-coupling reaction of alkyl halides with organomagnesium or organozinc reagents catalyzed by using a 1,3-butadiene as the additive. This reaction follows a new catalytic pathway: the Ni or Pd catalyst reacts first with R-MgX to form an anionic complex, which then reacts with alkyl halides. Bis-dienes were also effective additives for the Ni-catalyzed cross-coupling reaction of organozinc reagents with alkyl halides. This catalytic system tolerates a wide variety of functional groups, including nitriles, ketones, amides, and esters. In addition, we have extended the utility of Cu-catalyzed cross-coupling reactions. With 1-phenylpropyne as an additive, Cu-catalyzed reactions of alkyl chlorides, fluorides, and mesylates with Grignard reagents proceed efficiently. These new catalytic reactions use pi-carbon ligands such as pi-allyl units or alkynes instead of heteroatom ligands such as phosphines or amines. Overall, these reactions provide new methodology for introducing alkyl moieties into organic molecules.     

Stereoselective synthesis of substituted arylsulfonylated 1,3-butadienes and 2-propenoates by sulfonylation of acetylenic ester

Protonation of the reactive intermediates produced in the reaction between sodium arylsulfinates and two equiv. of dialkyl acetylenedicarboxylates in DMF, by H₂O lead to substituted (1E,3E)-1-(arylsulfonyl)-1,3-butadiene-1,2,3,4-tetracarboxylates in moderate yields. A regioselective method for the synthesis of alkyl (E)-3-(arylsulfonyl)-2-propenoates is described. These reactions provide a useful synthetic route to highly functionalized 1,3-butadienes and 2-propenoates.     

Untersuchungen zur elektrochemischen reduktion vinyloger carbonsäurechloride

Electrochemical reduction of vinylogous carbonic acid chlorides of the type ArCOCHCHCl (aryl 2-chlorovinyl ketones) has been studied using dc-polarography, cyclic voltammetry and coulometry at controlled potential. Preparative scale electrolyses yielded mainly 1,4-diaroyl-1,3-butadienes and 1,4-diaroyl-2-butenes, which thereby are accessible in a new way.     

金属试剂参与的α,β-不饱和羰基化合物的不对称共轭加成反应研究进展

α,β-不饱和化合物尤其是羰基化合物的不对称共轭加成反应在有机合成中是一类非常重要的反应。文章综述了格氏试剂、锌试剂以及芳基金属试剂和α,β-不饱和羰基化合物在铜或镍的催化作用下的不对称共轭加成反应。结果表明,金属试剂参与的该类反应,大都能够得到比较好的收率和选择性。同时,配体的研究开发对于该类反应的结果有着较大程度的影响。     

Formation of C-C Bonds via Ruthenium Catalyzed Transfer Hydrogenation: Carbonyl Addition from the Alcohol or Aldehyde Oxidation Level

Under the conditions of ruthenium catalyzed transfer hydrogenation employing isopropanol as terminal reductant, π-unsaturated compounds (1,3-dienes, allenes, 1,3-enynes and alkynes) reductively couple to aldehydes to furnish products of carbonyl addition. In the absence of isopropanol, π-unsaturated compounds couple directly from the alcohol oxidation level to form identical products of carbonyl addition. Such "alcohol-unsaturate C-C couplings" enable carbonyl allylation, propargylation and vinylation from the alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Thus, direct catalytic C-H functionalization of alcohols at the carbinol carbon is achieved.     

α,β-不饱和酮与金属有机试剂的不对称共轭加成反应的研究进展

综述了近来α,β 不饱和酮与金属有机试剂的不对称共轭加成反应的研究进展。详细介绍了α,β 不饱和酮与金属试剂反应的配体及影响反应的条件。     

Transition metal catalysed diboration

Homogeneous transition metal catalysed hydroboration reactions are discussed briefly, providing the background which led to the recent discovery of metal catalysed diborations [additions of the B–B bond in B₂(OR)₄ compounds] of alkynes, alkenes, 1,3-diynes, 1,3-dienes, and ά,βunsaturated ketones. Catalysed additions of B–Si and B–Sn bonds are also presented. Metal catalysed synthesis of organoboron compounds is a useful new synthetic method. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phosphoramidites: marvellous ligands in catalytic asymmetric conjugate addition

The development of an efficient catalytic system for enantioselective carbon-carbon bond formation by 1,4-addition of organometallic reagents (organolithium, Grignard, and organozinc reagents) to enones is a major challenge in organic synthesis. This Account presents the breakthrough realized in this field using chiral phosphoramidite ligands for copper-catalyzed dialkylzinc additions. Applications in catalytic routes to cycloalkanones as well as tandem and annulation procedures with excellent enantioselectivities are discussed.     

Synthesis and characterization of 2,3-dialkyl-1,4-butanediols and copolyesters containing these moieties

Summary Reaction of the 2,3-dimethylene-1,3-butadiene dianion (made using Lochmann's base) with a series of primary alkyl halides yielded 2,3-dialkyl-1,3-butadienes, which were converted to the corresponding 2,3-dialkyl-1,4-butanediols via hydroboration/oxidation. Along with ethylene glycol and dimethyl terephthalate these disubstituted butanediols were incorporated into copolyesters using melt condensation polymerization. The resultant copolymers were characterized by ¹H NMR, inherent viscosity, and DSC. From this data the effects of varying the length and amount of alkyl side groups on the copolyester syntheses and properties were studied.     

Calcium Chloride (CaCl2) as Catalyst for Asymmetric Organic Reactions

Pybox–CaCl₂ was found to be an efficient chiral catalyst for asymmetric 1,4-addition reactions of 1,3-dicarbonyl compounds with nitroalkenes, affording γ-nitro carbonyl compounds in high yields with high enantioselectivities. The reactions proceeded smoothly even in air, and were successfully applied to a continuous flow system.     

Preparation of substituted 5,6-dihydro-4H-1,3-oxazines from olefins

The 5,6-dihydro-4H-1,3-oxazine derivatives of methyl oleate and related compounds have been prepared. These novel six-membered heterocyclic compounds were obtained by the condensation of N-hydroxymethyl or N-chloromethylbenzamide with methyl oleate or its derivatives. These reactions can be regarded as 1,4-dipolar addition reactions. Presented at the AOCS-ISF World Congress in Chicago, October 1970. ARS, USDA.     

吡唑及其衍生物合成研究进展

综述了吡唑衍生物合成的研究进展。吡唑衍生物的合成方法有:(1)肼与1,3-二羰基酮发生反应;(2)重氮烷烃与烯炔化合物反应;(3)肼与乙酸乙酰乙酯反应;(4)肼与丙烯腈、丙二腈衍生物反应;(5)肼与烯酮反应;(6)在合成技术上还有固相合成和微波辅助合成等。     

Supported Catalysts Obtained by Interaction of Organometallic Compounds of Transition Elements with Oxide Supports

Rapid development of organometallic chemistry of transition elements in recent years has greatly influenced homogeneous catalysis. Many organometallic compounds of transition metals have been directly used as effective catalysts; e.g., π-ally1 complexes of transition elements for diene reactions [1–3], carbonyl complexes for hydroformilation [4], and cyclopentadienyl and arene complexes for hydrogenation [5]. The study of stoichiometric reactions of organometallic compounds was also of great importance for homogeneous catalysis as individual organometallic compounds of various classes represent the analogs of intermediate species formed in the process of catalytic reactions (e.g., π-complexes and σ-organometallic compounds [6–8] in various reactions where the original catalyst is not an organometallic compound).     

Supported Catalysts Obtained by Interaction of Organometallic Compounds of Transition Elements with Oxide Supports

Rapid development of organometallic chemistry of transition elements in recent years has greatly influenced homogeneous catalysis. Many organometallic compounds of transition metals have been directly used as effective catalysts; e.g., π-ally1 complexes of transition elements for diene reactions [1-3], carbonyl complexes for hydroformilation [4], and cyclopentadienyl and arene complexes for hydrogenation [5]. The study of stoichiometric reactions of organometallic compounds was also of great importance for homogeneous catalysis as individual organometallic compounds of various classes represent the analogs of intermediate species formed in the process of catalytic reactions (e.g., π-complexes and σ-organometallic compounds [6-8] in various reactions where the original catalyst is not an organometallic compound).     

Recent highlights in electrophilic fluorination with 1-chloromethyl-4-fluoro- 1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)

Synthetic and structural aspects of organofluorine compounds continue to be the focal points of vigorous research activities, as evidenced by the appearance of a large number of publications. Among the various useful methodologies for the introduction of fluorine into organic molecules, electrophilic fluorination is a promising and exciting area of research. While a variety of electrophilic fluorinating reagents are available, currently 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) provides a remarkably straightforward and effective route. The breadth of applications realizable from this reagent in its role as a key electrophilic fluorinating reagent is highlighted here. This Account covers the literature for electrophilic fluorination reactions that employ Selectfluor during the period January 1999-January 2003.     

Zirconocene and Si-tethered diynes: a happy match directed toward organometallic chemistry and organic synthesis

Characterizing reactive organometallic intermediates is critical for understanding the mechanistic aspects of metal-mediated organic reactions. Moreover, the isolation of reactive organometallic intermediates can often result in the ability to design new synthetic methods. In this Account, we outline synthetic methods that we developed for a variety of diverse Zr/Si organo-bimetallic compounds and Si/N heteroatom-organic compounds through the detailed study of zirconacyclobutene-silacyclobutene fused compounds. Two basic components are involved in this chemistry. The first is the Si-tethered diyne, which owes its rich reactive palette to the combination of the Si-C bond and the C≡C triple bond. The second is the low-valent zirconocene species Cp(2)Zr(II), which has proven very useful in organic synthesis. The reaction of these two components affords the zirconacyclobutene-silacyclobutene fused compound, which is the key reactive Zr/Si organo-bimetallic intermediate discussed here. We discuss the three types of reactions that have been developed for the zirconacyclobutene-silacyclobutene fused intermediate. The reaction with nitriles (the C≡N triple bond) is introduced in the first section. In this one-pot reaction, up to four different components can be combined: the Si-tethered diyne can be reacted with three identical nitriles, with differing nitriles, or with a nitrile and other unsaturated organic substrates such as formamides, isocyanides, acid chlorides, aldehydes, carbodiimides, and azides. Several unexpected multiring, fused Zr/Si organo-bimetallic intermediates were isolated and characterized. A wide variety of N-heterocycles, such as 5-azaindole, pyrrole, and pyrroloazepine derivatives, were obtained. We then discuss the reaction with alkynes (the C≡C triple bond). A consecutive skeletal rearrangement, differing from that observed in the reactions with nitriles, takes place in this reaction. Finally, we discuss the reaction with the C═X substrates (where X is O or N), including ketones, aldehydes, and isocyanides. Oxa- and azazirconacycles are formed via a new skeletal rearrangement. Our results show that the zirconocene and the Si-tethered diyne cooperate as a "chemical transformer" after treatment with various substrates, leading to a diverse range of cyclic Zr/Si organo-bimetallic compounds. This mechanism-derived synthesis of organometallic and organic compounds demonstrates that the investigation of metal-mediated reactions and the isolation of reactive organometallic intermediates not only contribute to the understanding of complex reactions but can also lead to the discovery of synthetically useful methods.     

Review on Greener and Safer Synthesis of Nitro Compounds

The review describes the recent developments in the green synthetic methods of nitro compounds involving environmentally benign approaches such as, use of solid‐supported reagents, microwave‐assisted reactions, ionic liquids, ultrasound assisted nitration reactions, gas phase nitration and vapor phase nitration.     

Activation of solid polymer surfaces with bifunctional reagents

An original procedure is described which calls upon the heterogeneous grafting of bifunctional molecules onto a reactive polymeric surface, leaving one of the functions available for further exploitation. The principle of this strategy is to use reagents characterised by a rigid planar structure bearing the two active moieties at opposite sites of the molecule. The examples provided include the reactions of lignocellulosic fibres with 1,4‐phenyl diisocyanate and 1,2,4,5‐benzenetetracarboxylic anhydride, which give rise to their surface activation through the incorporation of covalently bound isocyanate or anhydride functions. © 2001 Society of Chemical Industry     

Über die herstellung von poly-p-(ω-lithiumalkyl)-styrolen und ihre anwendung als polymere metallierungsmittel

Poly[p-(ω-lithium alkyl)styrene] with n = 1 to 4 were synthesized by reaction of the corresponding halogen compounds with n-butyl lithium. These organometallic polymers are useful metallating agents in interconversion reactions with halogen compounds as well as CH acidic substances, and their activity may be compared to that of n-butyl lithium. In halogen metal interconversion reactions the polymeric reagents may be used in many runs because their reactivation is easy to accomplish. However, some decrease of the number of active sites along the chain has been observed on account of WURTZ-FITTIG reactions between the polymer and the substrate.