MoCl5/EtAlCl2-catalysed nonmetathesis polymerization of norbornadiene

Norbornadiene was polymerized, in moderate yield by MoCl₅ or EtAlCl₂. By using both components together, an increase in reaction rates and in polymer yields were observed. By the optimization of the reaction conditions, 100% of polymer yield was achieved. For comparison, the polymerization of the NBD was also accomplished by using initiators such as AlCl₃, Et₃Al, AZBN, and n-butyl lithium. All the obtained polymers gave similar IR and NMR spectra indicating the presence of the polynortricyclene structures. Though they show different molecular weight distribution, the solubilities of the polymers (obtained using MoCl₅, AlCl₃, EtAlCl₂, and MoCl₅/EtAlCl₂) are very similar. DTA analyses show that the polymers (obtained by using MoCl₅/EtAlCl₂ pair or n-butyl lithium or Et₃Al) have high thermal stabilities whereas all the other polymers are unstable in air. © 1996 John Wiley & Sons, Inc.     

Reaction of crotonaldehyde with various ethyl aluminum chlorides in methylene chloride. A 1H-NMR study

The reactions of crotonaldehyde (CA) with ethyl aluminum chlorides have been examined using a titration technique at low temperature. The titrations were followed by ¹H-NMR spectroscopy. Evidence for complexes of the type (Et₂AlCl)₂CA and (Et₂AlCl-CA)₂ has been obtained. Ethyl aluminum sesquichloride undergoes sequential addition of CA to the EtAlCl₂ moiety, to the Et₂AlCl moiety, and again to the EtAlCl₂ moiety. Ethyl aluminum dichloride undergoes ligand redistribution, alternately disproportionating and reproportionating, the ultimate product being EtAlCl₂-CA₂.     

Cp2TiCl2-catalyzed synthesis of tetraalkyl-substituted pyrazines by the reaction of nitriles with EtAlCl2 and Mg

Tetraalkyl-substituted pyrazines were obtained by the multicomponent reaction of aliphatic linear nitriles with EtAlCl₂ in the presence of Mg and Cp₂TiCl₂ catalyst in 60–91% yields. The same processing of isobutyronitrile gave 2,4,5-triisopropyl-1H-imidazole in 56% yield.     

Synthesis of 1,2,3,4-tetrasubstituted aluminacyclopent-2-enes using Cp<Subscript>2</Subscript>ZrCl<Subscript>2</Subscript> as catalyst

Efficient procedures have been developed for the synthesis of 1,2,3,4-tetrasubstituted aluminacyclopent-2-enes via intermolecular cycloalumination of terminal olefins and acetylenes with EtAlCl₂ or cycloalumination of acetylenes with higher trialkylalanes in the presence of Cp₂ZrCl₂ as catalyst.     

Efficient synthesis of ferrocenylenones by Friedel-Crafts acylation with EtAlCl2-Me3Al

Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl₂ or EtAlCl₂-Me₃Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method.     

Combined cycloalumination of cyclic 1,2-dienes and olefins with EtAlCl2 in the presence of Cp2ZrCl2 catalyst

Catalytic intermolecular cycloalumination of cyclo-1,2-dienes and olefins assisted by EtAlCl₂ in the presence of Cp₂ZrCl₂ as catalyst gave rise to unsaturated di- and polycyclic aluminacarbocycles.     

Role of added Lewis base and alkylaluminum halide on living cationic polymerization of vinyl ether

In the living cationic polymerization of isobutyl vinyl ether (IBVE) by the CH₃CH (OiBu) OCOCH₃ ( 1 )/EtAlCl₂ initiating system in the presence of the added base in hexane at +40°C, the stability of the initiating system 1 /EtAlCl₂, which form initiating species CH₃CH^⊕ (OiBu) derived from 1 , was investigated. In the presence of the Lewis base such as ethyl acetate or 1,4-dioxane, the active species was stable for 300 min even at +40°C in the absence of IBVE, and the living polymers were quantitatively obtained by adding IBVE. However, the active species was partly consumed by side reactions during the standing time for 60 min in the presence of a less basic additive such as ethyl benzoate, and about 50% of the active species was deactivated in the presence of methyl chloroacetate. Consequently, in the case of a less basic additive such as methyl chloroacetate (which was effective for the fast living polymerization), it can be seen that the careful selection of polymerization conditions was required. The living polymerization rate was dependent on the second order of EtAlCl₂ concentration. EtAlCl₂ induced the cleavage of 1 into CH₃CH^⊕ (OiBu) and EtAl^?Cl₂(OCOCH₃), and the reactivity of CH₃CH^⊕ (OiBu) and propagating carbocation may be controlled by EtAl^?Cl₂(OCOCH₃) with the aid of other EtAlCl₂. Et_1.5AlCl_1.5 exists as a bimetallic complex of EtAlCl₂ and Et₂AlCl, and it is expected that the polymers having a bimodal molecular weight distribution will be obtained due to two kinds of counteranions coming from EtAlCl₂ and Et₂AlCl. However, in the cationic polymerization of IBVE by 1 /Et_1.5AlCl_1.5 in the presence of ethyl acetate, the living polymer exhibiting a unimodal and very narrow molecular weight distribution was obtained. Thereby, it was suggested that the counteranions, EtAl^?Cl₂(OCOCH₃) and Et₂Al^?Cl(OCOCH₃), exchange rapidly with each other. © 1994 John Wiley & Sons, Inc.     

Synthesis and transformations of metallacycles. 23. Cp2TiCl2-Catalyzed cyclometallation of fullerene C60 with EtAlCl2

1-Ethyl-2,3-fullerenoaluminacyclopropanes (EtAl)_n(²-C₆₀) were synthesized by the reaction of fullerene C₆₀ with an excess of EtAlCl₂ in the presence of Mg and using Cp₂TiCl₂ as the catalyst in a THF--toluene solution at 20 °C. Deuterolysis of fullerenoaluminacyclopropanes afforded a mixture of deuteriofullerenes C₆₀D_m, where m = 6--12.     

Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4-dioxane as an added base

The concentration ([P^*]) and lifetime (half-life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1-(isobutoxy) ethyl acetate [CH₃COOCH (OiBu) CH₃]/ethylaluminum dichloride (EtAlCl₂) system in the presence of excess 1,4-dioxane in n-hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether-type carbocation. The measurements were based on the end-capping reaction with sodiomalonic ester [Na^⊕?CH (COOEt)₂], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P^*] was determined by ¹H-NMR spectroscopy. In contrast to its constancy during the polymerization, [P^*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P^*], and the lifetime (half-life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl₂ concentration, and increasing dioxane concentration. In particular, the “base-stabilized” living ends, generated by the CH₃COOCH (OiBu) CH₃/EtAlCl₂/dioxane system, turned out extremely stable at 0°C (half-life > 5 days in the absence of monomer).     

Joint cycloalumination of ethylene and other unsaturated compounds with EtAlCl<Subscript>2</Subscript> in the presence of Cp<Subscript>2</Subscript>ZrCl<Subscript>2</Subscript>. Synthesis of aluminacarbocycles

A procedure has been developed for the selective synthesis of five-membered aluminum-containing heterocycles, 2,3-dialkyl-1-ethylaluminacyclopent-2-enes, 3-alkyl-1-ethylaluminacyclopentanes, 2-alkylidene-1-ethylaluminacyclopentanes, and 3-alkyl-1-ethyl-2-methylidenealuminacyclopentanes, via joint cycloalumination of ethylene and other unsaturated compounds (acetylenes, olefins, and allenes) with EtAlCl₂ in the presence of Cp₂ZrCl₂ as catalyst.     

Synthesis and conversions of metallocycles. 7. A novel approach to the synthesis of 3,4-dialkyl-substituted aluminacyclopentanes in the presence of Cp2ZrCl2

A novel approach was developed for the stereoselective synthesis of trans-3,4-dialkyl-substituted aluminacyclopentanes from -olefins, metallic magnesium, and EtAlCl₂ in the presence of catalytic amounts of Cp₂ZrCl₂. The hydrolysis and deuterolysis products of the 3,4-dialkyl-substituted aluminacyclopentanes obtained are only in the trans configuration.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1607–1609, July, 1991.     

High Pressure Lewis-Acid Catalyzed Diels-Alder Reactions of 3-Methyl-2-cyclopenten-1-one. A New Construction of Angularly Methylated Hydrindanones

The Diels-Alder reactions of 3-methyl-2-cyclopenten-1-one with simple acyclic dienes under high pressure in combination with EtAlCl₂ are described. Angularly methylated hydrindanones were isolated in reasonably to good yields. Structure analysis of the reaction products by NMR spectroscopy is presented.     

Synthesis and transformations of metallacycles 35. Joint cycloalumination of cyclic 1,2-dienes with disubstituted acetylenes and terminal allenes under the action of EtAlCl<Subscript>2</Subscript> catalyzed by Ti and Zr complexes

Catalytic intermolecular cycloalumination of cyclic 1,2-dienes with terminal allenes or disubstituted acetylenes mediated by EtAlCl₂ in the presence of complexes based on transition metals was accomplished. The yield of unsaturated bicyclic aluminacarbocycles was up to 85%.     

Preparation of Enantiomerically Pure β-Silylcarboxyl Derivatives by Asymmetric 1,4-Addition to N-Enoyl-sultams. Preliminary Communication

EtAlCl₂-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived ‘anti’ -aldols (via silyl-directed α-methylation).     

The first one-pot synthesis of alkoxycyclopropanes via cyclometalation of styrene with ClnAlEt3−n and RCO2R′ mediated by Cp2ZrCl2

The one-pot cyclopropanation of styrene using Cl_nAlEt_3−n (Et₂AlCl, EtAlCl₂, AlCl₃) and carboxylic esters in the presence of Cp₂ZrCl₂ as catalyst gives rise to alkoxycyclopropanes.     

Cycloalumination of α,ω-diolefins with EtAlCl<Subscript>2</Subscript> catalyzed by zirconium complexes

Cycloalumination of α,ω-diolefins was performed using EtAlCl₂ in the presence of metallic magnesium as halide ion acceptor and Cp₂ZrCl₂ as catalyst. The products were aluminacyclopentanes and carbocycles fused to aluminacyclopentane fragments.     

Asymmetric intramolecular Diels-Alder reactions of N-acyl-camphor-sultam trienes.

Treatment of triene-imides 4 with EtAlCl₂ at ?20° gave crystalline cycloadducts 5 which furnished enantiomerically pure bicyclic alcohols 9 with regeneration of the chiral auxiliary.     

An auxiliary induced asymmetric synthesis of functionalized cyclobutanes by means of catalytic (2+2)-cycloaddition reaction

A new entry to optically active hydroxycyclobutanes is described. Treatment of silyl enol ether and (−)-8-phenylmenthyl acrylate in the presence of a catalytic amount of EtAlCl₂ affords enantiomerically enriched multi-substituted cyclobutane compounds in a good yield and diastereofacial selectivity.     

Lewis acid-controlled reactions of zirconacyclopentadienes with isocyanates and isothiocyanates. One-pot three- or four-component synthesis of multiply substituted iminocyclopentadienes and butadiene-tethered 1,6-bisamides and electrophilic cyclization

Multiply substituted zirconacyclopentadienes including bicyclic zirconacyclopentadienes and zirconaindenes reacted with isocyanates and isothiocyanates in the presence of Lewis acids to afford iminocyclopentadienes and conjugated 1,6-bisamides, depending on the nature of Lewis acids, isocyanates, and isothiocyanates used. Only in the presence of BF₃ could iminocyclopentadienes be obtained in high isolated yields when zirconacyclopentadienes were treated with isocyanates. On the contrary, BF₃ could not mediate the reaction of zirconacyclopentadienes with isothiocyanates. For the reactions of zirconacyclopentadienes with isothiocyanates, EtAlCl₂ was found effective to generate iminocyclopentadienes as the products. Interestingly, however, for the reactions of zirconacyclopentadienes with isocyanates, EtAlCl₂ was found to work very differently from BF₃. Instead of iminocyclopentadienes, conjugated 1,6-bisamides and conjugated mono-amides were obtained as products in high isolated yields from the reactions of zirconacyclopentadienes with isocyanates, depending on the substituents of isocyanates. The reaction path and products could be controlled by Lewis acids. As a demonstration of the usefulness of thus obtained unsaturated bisamides, electrophilic cyclization using acids, NBS, and I₂ was carried out. Electrophilic cyclization of multisubstituted conjugated 1,6-bisamide derivatives afforded cyclic iminoethers in excellent yields with perfect selectivity. Only one of the amide groups took part in the electrophilic cyclization.     

The propagating species in living cationic polymerization: Living nature and steric structure of polymers

This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) [poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl-IBVE adduct (1)/ZnCl₂ system in a EtNO₂/CH₂Cl₂ mixture, whereas similar systems with EtAlCl₂ led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl₂ and 1/EtAlCl₂ were directly analyzed by ¹H NMR spectroscopy.