Search

Both intermolecular reactivities toward C-O and C-N unsaturated substrates and intramolecular reactions of various 1-lithio-1,3-dienes are briefly summarized. Results reveal that intramolecular synergy between the alkenyllithium moiety and the butadienyl skeleton make 1-lithio-1,3-diene derivatives useful and unique as building blocks in organic synthesis. It is demonstrated that substitution patterns and the nature of the substituents on the butadienyl skeleton have remarkable effects on reaction pathways. [ABSTRACT FROM AUTHOR]

Alkenylphosphines with various substituents were prepared by the reaction of an alkenylzirconocene with a chlorophosphine. Reactions of (α-unsubstituted alkenyl)zirconocenes with Ph2PCI or PhPCl2 gave the corresponding alkenyiphosphines in good yields. On the other hand, direct reactions of (α-unsubstituted alkenyl)zirconocenes with iPr2PCI did not proceed. Analogously, (α-substituted alkenyl)zirconocenes did not react with chlorophosphines directly. However, these reactions proceeded in the presence of CuCI affording the corresponding alkenylphosphines as CuCl complexes. Treatment of the copper complexes with Na2(dtc) (dtc = N,N-diethyldithiocarbamate) or Na4(edta) liberated free alkenylphosphines from the copper centers. The overall protocol could be applicable to preparation of a variety of alkenylphosphines from alkynes via alkenylzirconocene species. [ABSTRACT FROM AUTHOR]

Depending on the desilylation reagents used, 1-halo-1,4-bis(trimethylsilyl)-1,3-butadienes afforded either 1-halo-1-trimethylsilyl-1,3-butadienes or 1-halo-4-trimethylsilyl-1,3-butadienes in excellent yields with excellent selectivity, respectively, when treated with CF3COOH or with NaOMe. These monosilylated 1,3-butadiene products could be further desilylated to generate their corresponding halobutadienes via the above reagent-controlled desilylation reaction. When 1,4-dihalo-1,4-bis(trimethylsilyl)-1,3-dienes were treated with MeONa/MeOH at room temperature, desilylation of both of the two trimethylsilyl groups took place to afford their corresponding 1,4-dihalo-1,3-dienes in excellent yields. The commonly used desilylation reagent CF3COOH did not work for these dihalobutadienes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two one-pot multicomponent synthetic methods for highly substituted indenes are described. The intermolecular coupling of aromatic ketones with alkynes on low-valent zirconocene species generates oxazirconacyctopentenes, which upon hydrolysis with 20% HCl for 3 h afforded indene derivatives in good to excellent yields. Similarly, the pair-selective coupling of two identical or different alkynes bearing at least one aromatic substituent formed zirconacyclopentadienes. Quenching of the reaction mixture with concentrated H[sub 2]SO[sub 4] also results in the formation of highly substituted indenes in high yields. [ABSTRACT FROM AUTHOR]

Mediated by AlCl3, substituted spiro[4.5]deca-tetraenes underwent novel and selective skeletal rearrangement to generate indene derivatives in high to excellent yields. [ABSTRACT FROM AUTHOR]

Selective elimination from 1,3-dienic allylic carbonates occurs in the presence of a catalytic amount of [Ru(C5Me5)(4,4'-di-Bu'- 2,2'-bipyridine)(CH3CN)]PF6 and provides efficient access to a variety of [3]dendralenes. [ABSTRACT FROM AUTHOR]

Selective elimination from 1,3-dienic allylic carbonates occurs in the presence of a catalytic amount of [Ru(C5Me5)(4,4′-di-But-2,2′-bipyridine)(CH3CN)]PF6and provides efficient access to a variety of [3]dendralenes. [ABSTRACT FROM AUTHOR]

Mediated by CuCl, 1,4-dilithio-1,3-dienes reacted with carbon monoxide (CO) to generate multi-substituted cyclopentadienones and/or their head-to-head dimers, via tandem CO insertion and intra/intermolecular cycloaddition of organocopper compounds. [ABSTRACT FROM AUTHOR]

The combination of zirconocene-mediated coupling of silylated alkynes with a protonation—desilylation or bromination—desilylation process afforded otherwise unavailable butadiene derivatives. When (E,E)-2,3-dialkyl-1,4-bis(trimethylsilyl)-1,3-butadienes were treated with 3 equiv of Br2 in CH2Cl2, (E)-2,3-dialkyl-1,1,4,4-tetrabromo-2-butenes were obtained in excellent yields with perfect stereoselectivity. [ABSTRACT FROM AUTHOR]

Reports that one-pot reaction of carbon dioxide with 1,4-dilithio-1,3-diene derivatives created cyclopentadienone derivatives bearing various substituents in high yields within several minutes. Preparation of cyclopentadienone derivatives from corresponding diiodo compounds.

β-Hydrogen elimination from α-methylated bicyclic zirconacyclopentanes was promoted by benzaldehyde at low temperature. Treatment of the resulting mixture with allyl bromide and benzoyl chloride in the presence of CuCl introduced new olefin or phenylcarbonyl moieties in the product. [ABSTRACT FROM AUTHOR]

Reports on an unprecedented double C-C bond cleavage of a cyclopentadienyl ligand and the transformation of the resulting two pieces into a benzene derivative and a pyridine derivative. Reaction of titanacyclopentadiene; Synthesis of a tetraethyltitanacyclopentadiene with one methylcyclopentadienyl ligand and a pentadeuterated Cp ligand.

Organolithium compounds can behave as reductants but never as oxidants in redox reactions. Reported herein is that 1,4-dilithio-1,3-butadienes reacted with [Ni(cod)2] (cod=1,5-cyclooctadiene) to deliver dilithionickeloles. Single-crystal Xray structural analysis revealed a coplanar structure of dilithionickeloles with an averaging of bond lengths. XPS data confirmed the oxidation state of Ni in dilithionickeloles was Ni2+. 7Li NMR spectra of dilithionickeloles and theoretical calculations revealed a considerable aromatic character. In this redox reaction, the dilithio dianionic compounds behaved as formal oxidants, thus oxidizing Ni0 into Ni2+. These results demonstrated that organolithium compounds with π-conjugation could be used as oxidants and could continue to accept extra electrons. [ABSTRACT FROM AUTHOR]

Organolithium compounds can behave as reductants but never as oxidants in redox reactions. Reported herein is that 1,4-dilithio-1,3-butadienes reacted with [Ni(cod)2] (cod=1,5-cyclooctadiene) to deliver dilithionickeloles. Single-crystal X-ray structural analysis revealed a coplanar structure of dilithionickeloles with an averaging of bond lengths. XPS data confirmed the oxidation state of Ni in dilithionickeloles was Ni2+. 7Li NMR spectra of dilithionickeloles and theoretical calculations revealed a considerable aromatic character. In this redox reaction, the dilithio dianionic compounds behaved as formal oxidants, thus oxidizing Ni0 into Ni2+. These results demonstrated that organolithium compounds with β-conjugation could be used as oxidants and could continue to accept extra electrons. [ABSTRACT FROM AUTHOR]

A new method for the in situ generation of five-membered diamidocarbenes (DACs 2) from 2,2-dichloroimidazolidine-4,5-diones is established by Cl/I exchange and elimination of iodine. The trapping of 2 with CuI, S, and Se provides a good route for the preparation of a dimeric (2a)CuI complex and 2-thioxo/selenoxoimidazolidine-4,5-diones, respectively. In contrast, Cl/F exchange is explored to yield exclusively 2,2-difluoroimidazolidine-4,5-diones. [ABSTRACT FROM AUTHOR]

The t-BuCN-stabilized zirconacyclopropene-azasilacyclopentadiene complexes 2 are generated in situ in high yields from the Si-tethered diynes, Cp2Zr(ll) species, and 2 equiv of t-BuCN via a coordination-induced Zr-C/Si-C bond cleavage and reorganization. Complexes 2 have been demonstrated to be synthetically very useful. A variety of novel Zr/Si organo-bimetallic compounds and Si/N heterocyclic compounds, such as azasilacyclopentadienes, azasilacyclohexadienes, and allenylazazirconacycles, are obtained in high yields when complexes 2 are treated with ketones, carbodiimides, alkynes, elemental sulfur (S8), acid chlorides, or nitriles. In this chemistry, t-BuCN behaves as both an initiator and a brake/release handle to initiate and control the reaction process. [ABSTRACT FROM AUTHOR]

The article presents the study which demonstrated the efficient one-pot synthesis of dihydropyrimidinthiones through multicomponent coupling of several elements such as terminal alkynes, elemental sulfur, and carbodiimides. It says that the study has able to demonstrate an organolithium-promoted multicomponent reactions (MCRs) that involved various elements. It adds that the study offers a pathway to 2,3-dihydropyrimidinthiones that may have significant biological activity.

Transition-metal-mediated reaction of organonitriles has attracted much attention, since novel reaction patterns of the carbon (C) and nitrogen (N) triple bonds can be developed and synthetically useful methodologies for construction of C-C single bonds, C-N single bonds, and C-O single bonds can be expected. Particularly, transition-meta-mediated coupling of organonitriles with other unsaturated organic substrates such as alkynes is of great synthetic interest. This article focuses on a zirconocene-rnediated coupling reaction of organonitriles with alkynes, in which one Si-tethered diyne 1 is coupled in one pot with three molecules of nitriles promoted by a low-valent zirconocene species.