A new approach to construction of isoindolo[1,2-a]isoquinoline alkaloids Nuevamine, Jamtine, and Hirsutine via IMDAF reaction

The interaction between 1-furyl-1,2,3,4-tetrahydroisoquinolines and unsaturated acids derivatives (acryloyl, methacryloyl, and crotonoyl chloride, maleic and citraconic anhydride) was studied. It was shown that the reaction proceeds via amide formation and subsequent intramolecular Diels-Alder reaction of the furan (IMDAF). The [4+2] cycloaddition proceeded under mild reaction conditions (25-80 °C) and afforded only the exo-adduct in a high yield. With this method, a new approach to the isoindolo[1,2-a]isoquinoline system, the basic structural element of alkaloids Jamtine, Hirsutine, and Nuevamine, is proposed.     

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.     

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.     

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.     

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.     

Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: scope and limitations

The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br₂/I₂) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF.     

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.     

Asymmetric O-methylhalohydrin reaction of chiral N-enoyl-2-oxazolidinones: synthesis of N-protected syn-β-methoxyphenylalanine, an unusual amino acid component of cyclomarins

Asymmetric O-methylhalohydrin reactions of chiral N-enoyl-2-oxazolidinones were performed with halogens (Br₂/I₂) promoted by silver(I) in methanol with high regio- and anti-selectivity and moderate to good diastereoselectivity. Reagent-controlled opposite diastereoselectivity was observed especially for cinnamoyl and electron-deficient cinnamoyl substrates. This method was applied to the short enantioselective synthesis of N-protected syn-β-methoxyphenylalanine, an unusual amino acid component of cyclomarins.     

Synthesis and transformations of metallacycles. 28. Reactions of allenes with EtAlCl2 and Et2AlCl catalyzed by Ti and Zr complexes

Catalytic cycloalumination of allenes with EtAlCl₂ in the presence of Ti or Zr complexes afforded methylidene- and alkyl(benzyl)idenealuminacyclopropanes and the corresponding aluminacyclopentanes, which were identified by analyzing the hydrolysis products. The reactions with the use of Et₂AlCl instead of EtAlCl₂ produced 1,2- and 1,4-dialuminum compounds.     

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).     

The reactions of nickel(II) carboxylates with a series of ethylaluminum chlorides

The distribution of nickel in the reaction products from the reactions of nickel(II) stearate with diethylaluminum chloride (Et₂AlCl), ethylaluminum sesquichloride (Et₃Al₂Cl₃), and ethylaluminum dichloride (EtAlCl₂) in benzene was investigated as a function of the Al/Ni reaction stoichiometry. The products consist of benzene-soluble nickel complexes and a precipitate from which can be extracted NiCl₂ and metallic nickel. The percentage of each product is seen to be dependent upon the Al/Ni reaction ratio and the aluminum compound employed in the reaction. It was found that in each case six alkylaluminums are required for complete reaction with one nickel(II) stearate molecule. The compunds Et₂AlCl, Et₃Al₂Cl₃, and EtAlCl₂ were all found to have greater reducing ability than Et₃Al at room temperature. Alternative interpretations of the chloro compounds' greater reducing abilities are discussed.     

Acylation of N-p-toluenesulfonylpyrrole under Friedel-Crafts conditions: evidence for organoaluminum intermediates

The Friedel-Crafts acylation of N-p-toluenesulfonylpyrrole under Friedel-Crafts conditions has been reinvestigated. Evidence is presented in support of the hypothesis that when AlCl₃ is used as the Lewis acid, acylation proceeds via reaction of an organoaluminum intermediate with the acyl halide. This leads to the production of the 3-acyl derivative as the major product. With weaker Lewis acids (EtAlCl₂, Et₂AlCl) or less than 1 equiv of AlCl₃ the relative amount of 2-acyl product is increased. A mechanistic rationalization is presented to explain these data.     

Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis, characterization and catalytic oligomerisation of ethylene

New N-functionalised 2-phosphinobenzaldimino (P^N) ligands bearing 3-picolyl, furfuryl, thiophene-2-methyl, thiophene-2-ethyl, and benzyl groups have been prepared in good yield. The 2-phosphinobenzaldimino ligands were reacted with PdCl₂(COD) to give the corresponding metal complexes of the type Pd(L)Cl₂ (L = 2-phosphinobenzaldimino (P^N) ligand). All compounds were fully characterized using spectroscopic and analytical techniques, including ¹H, ¹³C, and ³¹P NMR and IR spectroscopies, mass spectrometry and elemental analysis. Selected neutral palladium complexes were evaluated as catalyst precursors in ethylene oligomerisation reactions, after activation with a co-catalyst (MMAO, EtAlCl₂, or Et₂AlCl).     

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.     

Telomeres photoreticulables—1. Synthese de telomeres photoreticulables a partir du cinnamate et de l'acetate de vinyle

Photocrosslinkable telomers containing cinnamoyl groups can be prepared by two methods, viz, (i) direct telomerisation of vinyl cinnamate using either redox initiation (FeCl₃ benzoin-CuCl₂) or conventional radical initiation (benzoyl peroxide), and (ii) esterification of polyvinylalcohol telomers with cinnamoyl chloride. The former method gives products which are extensively cyclised, as indicated by i.r. and NMR spectra, whereas the latter method gives materials in which all the cinnamoyl groups are available for crosslinking.     

Massenspektrometrische Untersuchung von Amiden. VI—Mechanismus der Methyl-Abspaltung aus Crotonsä;urepiperidid

By the investigation of ²H labelled compounds, it has been established that in the case of crotonoyl piperidyl only the hydrogens of the methyl group participate in the elimination of CH₃·.     

“LIVING-LIKE” CATIONIC POLYMERIZATION OF ISOBUTYL VINYL ETHER INITIATED BY CARBOXYL GROUPS ON CARBON BLACK SURFACE/ETHYLALUMINUM DICHLORIDE SYSTEM IN THE PRESENCE OF 1,4-DIOXANE

The effect of 1,4-dioxane as an added base on the cationic polymerization of isobutyl vinyl ether (IBVE) initiated by carboxyl groups on carbon black surface/ethylaluminum dichloride (EtAlCl₂) system was investigated. Although the cationic polymerization of IBVE by carbon black/EtAlCl₂ system the absence of 1,4-dioxane instaneously proceeded and the monomer conversion achieved 100% within a minute. The molecular weight distribution (MWD) of polyIBVE obtained was very broad. On the contrary, the MWD of polyIBVE obtained was very narrow and narrower than that obtained from the carbon black/ZnCl₂ initiating system by the addition of 1,4-dioxane. The number-average molecular weight (Mn) of polyIBVE obtained was directly proportional to monomer conversion in the cationic polymerization. However, the Mn of polyIBVE obtained from the polymerization by the initiating system in the the presence of 1,4-dioxane was smaller than that of the calculated value, assuming that polyl(IBVE) chain forms per unit carboxyl group on carbon black surface. It was concluded that carbon black/EtAlCl₂ initiating systems in the presence of 1,4-dioxane has an ability to initiate “living-like” cationic polymerization of IBVE based on the above results. PolyIBVE was grafted onto a carbon black surface after quenching the above “living-like” cationic polymerization systems with methanol.     

Diastereoselective Alkyl Grignard 1,4‐Additions to para‐Substituted (2R)‐N‐Cinnamoylbornane‐10,2‐sultam Derivatives: Influence of N‐Atom Pyramidalization

Several typical ¹³C‐NMR displacements (of C?O, C(α), C(β), and C_ipso), as well as conformational or energy properties (S? N? C?O dihedral angle, ΔE syn/anti; HOMO/LUMO) could be correlated with the electronic parameters of p‐substituted N‐cinnamoylbornane‐10,2‐sultams 2 . Even under nonchelating conditions, the pyramidalization of the sultam N‐atom decreases for electron‐attracting p‐substituents, inducing a modification of the sultam‐ring puckering. Detailed comparison of the X‐ray structure analyses of 2b, 2d , and 2m showed that the orientation of the sterically directing pseudo‐axial S?O(2) and H? C(2) is modified and precludes any conclusion about the π‐facial stereoelectronic influence of the N lone pair on the alkyl Grignard 1,4‐addition. We also showed that the aggregating alkyl Grignard reagent may be used in equimolar fashion, demonstrating that the sultam moiety is chelated with a Lewis acid such as MgBr₂. The Schlenk equilibrium may also be used to generate the appropriate conditions of effective 1,4‐diastereoselectivity. Although the anti‐s‐cis/syn‐s‐cis difference of conformational energies for N‐cinnamoyl derivatives 2 is higher than for the simple N‐crotonoyl analogue, an X‐ray structure analysis of the SO₂/C?O syn derivative 10 confirms the predictive validity of our conformational calculations for ΔE≤1.8 kcal/mol.     

Controlled synthesis of glycopolymers with pendant D-glucosamine residues by living cationic polymerization

D -glucosamine-containing glycopolymers with well-controlled structure were synthesized by living cationic polymerization. To this end, D -glucosamine-containing vinyl ether (VE) of the type [CH₂()CH(OCH₂CH₂OR)] was prepared, where R denotes a 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimide-β-D -glucopyranoside, i.e., the hydroxyl and amino groups in D -glucosamine residues are protected by acetyl and phthaloyl groups, respectively. It was found that (1) the efficient living cationic polymerization of VE monomer is achieved by a combination of ethylaluminum dichloride (EtAlCl₂) with an adduct of trifluoroacetic acid (TFA) and isobutyl VE (IBVE) [CH₃CH(OiBu)OCOCF₃] (i.e., TFA/EtAlCl₂ initiating system); and (2) the polymerization in toluene at the elevated temperature (0°C) is most suitable to proceed the homogeneous polymerization over the whole conversion range. The molecular weight distribution of the resulting polymers was very narrow ($ {\bar M}_w/{\bar M}_n \sim 1.1 $). Quantitative deprotection of the resulting precursor polymers was successfully achieved with hydrazine monohydrate to afford the corresponding water-soluble polymers with pendant D -glucosamine residues. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 751–757, 1997     

One-pot synthesis of 2,3,5-substituted 1H-pyrroles via the reaction of terminal acetylenes with nitriles and EtAlCl2 catalyzed by Сp2TiCl2

A new one pot method for the synthesis of 2,3,5-substituted 1H-pyrroles in moderate to good yields (58–77%) based on multicomponent reaction of terminal acetylenes with nitriles and EtAlCl₂ in the presence of Сp₂TiCl₂ catalyst and metallic magnesium has been developed. The possible mechanistic pathway to substituted pyrroles is discussed.