Bifunctional Phase-transfer Catalysts Research Articles

Asymmetric Mannich reaction of N-Boc aminosulfones with 3-methylbenzofuran-2 (3H) - Ones catalyzed by a chiral phase-transfer catalyst

An enantioselective Mannich reaction of N-Boc aminosulfones with 3-methylbenzofuran-2 (3H)-ones catalyzed by a quinine-derived bifunctional phase transfer catalyst was developed, by which a series of chiral benzofuranones bearing adjacent quaternary and tertiary carbon centers were obtained in high yields (up to 96%) with good diastereoselectivities (up to >99:1) and enantioselectivities (up to 98%).

Chiral bifunctional organocatalysts for enantioselective synthesis of 3-substituted isoindolinones.

A series of chiral bifunctional organocatalysts were prepared and used for enantioselective synthesis of 3-substituted isoindolinones from 2-formylarylnitriles and malonates through aldol-cyclization rearrangement tandem reaction in excellent yields and enantioselectivites (up to 87% yield and 95% ee) without recrystallization. In this investigation, we found that chiral tertiary-amine catalysts with a urea group can afford 3-substituted isoindolinones both in higher yields (87% vs. 77%) and enantioselectivities (95% ee vs. 46% ee) than chiral bifunctional phase-transfer catalysts.

New anionic cobalt(III) complexes enable enantioselective synthesis of spiro-fused oxazoline and iodoacetal derivatives.

Anionic salicylimine-based cobalt (III) complexes featuring chiral ligands derived from isoleucine amino acids were used as efficient bifunctional phase-transfer catalysts for electrophilic iodination of enol ethers. The Brønsted acids of these complexes enabled the enantioselective asymmetric iodocyclization of enol ethers, furnishing spiro-fused oxazoline derivatives in high yields with up to 90:10 er. In addition, chiral cobalt (III) complexes catalyze the asymmetric intermolecular iodoacetalization of enol ethers with various alcohols to afford 3-iodoacetal derivatives in high yields with up to 92:8 er.

Bifunctional phase-transfer catalysts for synthesis of 2-oxazolidinones from isocyanates and epoxides.

A series of bifunctional phase-transfer catalysts (PTCs) were synthesized to catalyze the [3 + 2] coupling reaction of isocyanates and epoxides to afford 2-oxazolidinones in good to high yields (up to 92% yield) using PhCl as a solvent at 100 °C within 12 h. These bifunctional PTCs were easily prepared from commercially available tertiary-primary diamines and isocyanates (or isothiocyanates, mono-squaramides, respectively) in two simple steps with good modularity and demonstrated high efficiency (2.5 mol% catalyst-loading). The synergistic interaction of the quaternary ammonium salt center and hydrogen-bond donor group in the catalyst with the substrate is crucial to this atom-economic reaction.

Phase-Transfer-Catalyzed, Enantioselective Vinylogous Conjugate Addition-Cyclization of Olefinic Azlactones To Access Multifunctionalized Chiral Cyclohexenones.

An asymmetric, phase-transfer-catalyzed vinylogous conjugate addition-vinylogous cyclization cascade of olefinic azlactones with 4-nitro-5-styrylisoxazoles is reported. In the presence of an l- tert-leucine-derived urea-quaternary ammonium salt as a bifunctional phase-transfer catalyst and KF, two series of valuable optically pure cyclohexenones featuring two and three stereocenters were obtained in high yields with good to excellent enantio- and diastereoselectivities.

L-tert-Leucine derived urea-ammonium salts: Efficient bifunctional phase transfer catalysts for highly diastereo- and enantioselective aza-Henry reaction of isatin-derived N-Boc ketimines with α-aryl nitromethanes

An efficient way of aza-Henry reaction between isatin-derived N-Boc ketimines and α-aryl nitromethanes catalyzed by bifunctional phase transfer catalysts with a quaternary ammonium center derived from L-tert-Leucine has been developed. A series of 3-substituted 3-amino-oxindoles were constructed by this catalytic protocol in excellent yields (90–99%), with high enantioselectivities (83–95%) and diastereoselectivities (79:21–97:3). The asymmetric aza-Henry reaction of N-Boc amidosulfones and α-aryl nitromethanes were also investigated and gave the corresponding products in high to excellent yields (72–97%) with high enantioselectivities (up to 99%) and diastereoselectivities (up to >99:1).

Chiral Bifunctional Phase-Transfer Catalysts for Asymmetric Aminations

Key words phase-transfer catalysis - asymmetric catalysis - amination - chiral bifunctional catalyst

Bifunctional phase-transfer catalysts for fixation of CO2 with epoxides under ambient pressure

A series of bifunctional phase-transfer catalysts with a quaternary onium center and a hydrogen-bonding donor group were prepared for the fixation of CO2 with epoxides under mild conditions by using a CO2 balloon (1 atm) to produce cyclic carbonates up to 95% yields.

Design of Efficient Chiral Bifunctional Phase-Transfer Catalysts Possessing an Amino Functionality for Asymmetric Aminations

An efficient, chiral bifunctional phase-transfer catalyst with an intramolecular amino functionality has been designed and successfully applied to highly enantioselective amination of 3-aryloxindoles and 3-arylbenzofuran-2(3H)-ones with bis(adamantyl) azodicarboxylate. Optically active amination products were generally obtained in high yield with high enantioselectivity. The origin of stereoselectivity was explained by means of the DFT calculations.

Enantioselective intermolecular iodoacetalization of enol ethers catalyzed by chiral Co(III)-complex-templated Brønsted acids

The chiral Co(III)-complex-templated Brønsted acids were used as efficient bifunctional phase-transfer catalysts for the asymmetric intermolecular iodoacetalization of enol ethers, such as 3,4-dihydro-2H-pyran, 2,3-dihydrofuran, ethyl vinyl ether with alcohols and NIS, furnishing the 3-iodoacetals in high yield with up to 83:17 er.

Enantioselective Bromocyclization of Tryptamines Induced by Chiral Co(III)-Complex-Templated Brønsted Acids under an Air Atmosphere.

The chiral Co(III)-complex-templated Brønsted acids were found to be efficient bifunctional phase-transfer catalysts for the highly enantioselective bromocyclization of protected tryptamines with readily available N-bromosuccinimide (NBS) under an air atmosphere. The 3-bromohexahydropyrrolo[2,3- b]indoles, which are key building blocks of cyclotryptamine alkaloids, were thus obtained in up to 95% yield and 93.5:6.5 er.

Enantioselective Alkylation of 2-Oxindoles Catalyzed by a Bifunctional Phase-Transfer Catalyst: Synthesis of (-)-Debromoflustramine B.

A new bifunctional phase-transfer catalyst that employs hydrogen bonding as a control element was developed to promote efficient enantioselective SN 2 reactions for the construction all-carbon quaternary stereocenters in high yield and excellent enantioselectivity (up to 97 % ee) utilizing the alkylation of a malleable oxindole substrate. The utility of the methodology was demonstrated through a concise and highly enantioselective synthesis of (-)-debromoflustramine B.

Enantioselective amination of nitroolefins under base-free and water-rich conditions using chiral bifunctional phase-transfer catalysts.

The direct enantioselective amination of nitroolefins has been performed with l-tert-leucine-derived squaramide-scaffold bifunctional phase-transfer catalysts under base-free and water-rich conditions with low catalyst loading (0.5-1 mol%) to provide 2-aminonitroalkanes in good yields (up to 96%) and enantioselectivities (up to 93% ee).

Switchable Stereoselectivity in Bromoaminocyclization of Olefins: Using Brønsted Acids of Anionic Chiral Cobalt(III) Complexes.

Brønsted acids of anionic chiral CoIII complexes act as bifunctional phase-transfer catalysts to shuttle the substrates across the solvent interface and control stereoselectivity. The diastereomeric chiral CoIII -templated Brønsted acids, with the same chiral ligands, enabled a switch in the enantioselective bromoaminocyclization of olefins to afford the two enantiomers of 2-substituted pyrrolidines with high enantioselectivities (up to 99:1 e.r.).

Effective asymmetric vinylogous Mannich reaction of isatin imines with α,α-dicyanoolefins in the presence of a simple chiral amide phosphonium bifunctional phase transfer catalyst

A Mannich reaction between N-Boc isatin imine and α,α-dicyanoolefin as well as subsequent oxidative cleavage of the malonic nitrile moiety were described.

Highly enantioselective nitro-Mannich reaction of ketimines under phase-transfer catalysis

A novel bifunctional phase-transfer catalyst 1i was found to be highly efficient for the nitro-Mannich reaction of unactivated ketone-derived imines with the introduction of the protecting group 6-methyl-2-pyridylsulfonyl to the ketimines. Density functional theory (DFT) calculations are also performed to give the possible transition-state model.

Enantioselective Alkylative Kinetic Resolution of 2-Oxindole-Derived Enolates Promoted by Bifunctional Phase Transfer Catalysts

The first strategy for bringing about highly enantioselective alkylative enolate kinetic resolutions using a simple phase-transfer protocol via SN2 chemistry has been developed. In the presence of a new squaramide-based quaternized cinchona alkaloid-derived catalyst and aqueous base, benzyl, allyl, and propargyl halides react with racemic substituted oxindoles to generate densely functionalized products with the two contiguous stereocenters, one of which is an all-carbon quaternary.

Amide-Phosphonium Salt as Bifunctional Phase Transfer Catalyst for Asymmetric 1,6-Addition of Malonate Esters to para-Quinone Methides.

Asymmetric 1,6-addition of malonates to para-quinone methides has been developed by using amide-phosphonium salts derived from easily available chiral α-amino acids as bifunctional phase transfer catalysts. Stabilized para-quinone methides with various substituents on the phenyl ring were reacted with diphenyl malonates to give functionalized diaryl methines in excellent yields and high to excellent ee's. Furthermore, to show the utility of this methodology, a gram scale synthesis of an 1,6-addition adduct and its further elaboration into the key intermediate for synthesis of GPR40 agonists were also described.

Phase-Transfer Catalysis via a Proton Sponge: A Bifunctional Role for Biscyclopropenimine.

The use of a bis(diisopropylamino)cyclopropenimine-substituted bis-protonated proton sponge as a bifunctional phase-transfer catalyst is reported. Experimental studies and DFT calculations suggest it operates simultaneously as a hydrogen bond donor and a phase-transfer catalyst, facilitating the movement of charged intermediates from the interface to the organic phase via favorable partitioning of hydrophilic/hydrophobic surface areas, resulting in high catalytic activity.

ChemInform Abstract: Cascade Reactions of Glycine Schiff Bases and Chiral Phase Transfer Catalysts in the Synthesis of α‐Amino Acids 3‐Substituted Phthalides or Isoindolinones.

The tuning of aldol/cyclization cascade reactions of glycine Schiff bases with 2-cyano benzaldehydes provides access to non-natural α-amino acid derivatives substituted alternatively with phthalides or isoindolinones, depending on the strength of the used base. Moreover, a preliminary screening of catalysts and conditions for development of asymmetric versions identified chiral bifunctional phase transfer catalysts as particularly promising, leading to the α-amino esters 3-substituted phthalides in high yields and good diastereo- and enantioselectivity.