The carbocationic polymerization of isobutylene (IB), co-initiated by GaCl 3 or FeCl 3 ·dialkyl ether 1:1 complexes has been investigated in hexanes in the −20 to 10°C temperature range. In contrast to AlCl 3 ·diisopropyl ether (AlCl 3 ·i-Pr 2 O) complexes, 1 GaCl 3 ·i-Pr 2 O and FeCl 3 ·i-Pr 2 O readily co-initiate polymerization with 2-chloro-2,4,4-trimethylpentane (TMPCl) or tert-butyl chloride (t-BuCl) in the presence or absence of proton trap. In the absence of proton trap, chain transfer to monomer readily proceeded, resulting in close to complete monomer conversion and up to 85% exo-olefinic end group content. Diisopropyl ether complexes gave the highest polymerization rates, while nonbranched alkyl ether complexes were completely inactive. A polymerization mechanism is proposed to involve ether-assisted proton elimination to yield PIB exo-olefin, and the abstracted proton can subsequently start a new polymer chain by protonation of IB. Alternatively PIB + may be deactivated by ion collapse to yield PIBCl, which can be reactivated by the Lewis acid. The reasons for the difference in behavior between the Ga and Fe catalysts and the Al-based catalysts are described. ■ INTRODUCTIONLow molecular weight (M n ∼ 500−5000 g/mol) olefin end functional PIB is a precursor to motor oil and fuel additives. Currently two major industrial methods are utilized to produce low molecular weight IB homo or copolymers with olefinic end groups. The "conventional" method uses a C4 mixture and AlCl 3 or EtAlCl 2 based catalyst systems, which provides polybutenes with high trisubstituted olefinic content. 2,3 The other method employs pure IB and uses BF 3 complexes with either alcohols or ethers as catalysts, yielding highly reactive PIB (HR PIB) with high exo-olefinic end-group content. 4 In contrast to the trisubstituted olefins of conventional polybutenes, PIB exo olefins readily react with maleic anhydride in a thermal ene reaction to produce PIB succinic anhydride and subsequently polyisobutenyl succinimide ashless dispersants. Since chlorination is not necessary for maleation of HR PIB, the final product does not contain any chlorine, making HR PIB more desirable than conventional polybutenes.In recent decades, several new methods for the synthesis of HR PIB have been reported. For example, PIBCl was selectively dehydrochlorinated by a bulky base, e.g., potassium tertbutoxide to yield HR PIB. 5 Storey et al. used living cationic polymerization of IB at −80°C to obtain living PIB, which was then end-quenched with sterically hindered bases 6 or sulfides. 7 Another method used to produce HR PIB, developed by Kuhn and co-workers, involves inorganic/organometallic catalysts with weakly coordinating anions in dichloromethane (DCM). 8 Recently, Kostjuk and Wu independently reported that at moderate temperatures AlCl 3 ·dibutyl ether 9 (AlCl 3 ·Bu 2 O) and AlCl 3 ·i-Pr 2 O 10 complexes in DCM or DCM/hexanes 80/20 (v/ v) mixtures give HR PIB with exo-olefinic end-groups in excess of 90%. Shortly thereafter, Wu and co-workers also rep...

No abstract

The simple α,β-unsaturated ketones and 2-pyrones are readily available and synthetically important dienophiles and dienes, respectively, for Diels−Alder reactions. However, both prove to be challenging substrates for catalytic asymmetric Diels−Alder reactions. By exploring a new catalysis strategy featuring cooperative catalysis with readily available cinchona catalysts, an unprecedented asymmetric Diels−Alder reaction of simple α,β-unsaturated ketones with 2-pyrones has been successfully developed. With broad scopes for both reactants, the reaction provides a direct and versatile asymmetric access to a wide range of structurally novel bicyclic chiral building blocks amenable for further synthetic elaborations.

New phase transfer catalysts are reported for the first example of an organocatalytic asymmetric conjugate addition of cyanide with acetone cyanohydrin. Utilizing an accessible cupreidinium salt and a cyanation reagent suitable for industrial scale, this reaction holds significant promise for practical asymmetric synthesis. Additionally, the reported catalysts were developed as a result of gaining key structural insights via X-ray analysis of a series of catalysts of varying efficiencies and asymmetric induction.

A class of easily accessible and readily tunable chiral phase transfer catalysts based on 6’-OH cinchonium salts was found to efficiently catalyze an unprecedented highly enantioselective Darzens reaction of α-chloro ketones and aldehydes, which directly produces optically active chiral epoxides from readily available carbonyl compounds.