Dynamic kinetic resolution of azlactones catalyzed by chiral Brønsted acids

Chiral Br?nsted acids have been shown for the first time to catalyze the dynamic kinetic resolution of azlactones. 3,3'-Bis-(9-anthryl)-BINOL phosphoric acid 3c is particularly effective in the case of 4-aryl-substituted substrates, producing 85-92% ee's.     

Enantioselective direct aza hetero-Diels-Alder reaction catalyzed by chiral Brønsted acids

[Structure: see text] The first chiral Br?nsted acid-catalyzed asymmetric direct aza hetero-Diels-Alder reaction has been described. The phosphoric acids, prepared from binol and H8-binol derivatives, have shown catalytic ability for the reaction of cyclohexenone with N-PMP-benzaldimine. A chiral phosphoric acid, derived from 3,3-di(4-chloropheneyl)-H8-binol, exhibited superior enantioselectivity, affording fairly good yields and enantioselectivities for the reaction of a range of aromatic aldimines with cyclohexenone.     

Aza-Diels–Alder reaction catalyzed by novel chiral metalocomplex Brønsted acids

A series of Co(III) anionic complexes of Schiff bases obtained from salicylaldehydes and enantiomerically pure amino acids has been synthesized. The outersphere counterion was exchanged by H⁺ and the novel chiral Brønsted acids were used to induce asymmetry into an aza-Diels–Alder reaction. The influence of the temperature, solvent polarity, and structural modification of the chiral anions on the enantioselectivity of the process has also been investigated.     

Enantioselective oxysulfenylation and oxyselenenylation of olefins catalyzed by chiral Brønsted acids

This paper describes Brønsted acid catalyzed enantioselective oxysulfenylation and oxyselenenylation of olefins. Enantiomerically enriched tetrahydrofurans are formed with up to 63% ee with dibenzoyl-d-tartaric acid and its derivatives as catalyst. Chiral β-carboxyl sulfides and selenides have also been obtained with up to 50% and 84% ee, respectively, via enantioselective desymmetrization of thiiranium and seleniranium ions in the presence of catalytic amounts of chiral binaphthol derived N-triflyl phosphoramide.     

Asymmetric dearomatization enabled by chiral Brønsted acid activation of ynamides

Science China Chemistry -     

An enantioselective chiral Brønsted acid catalyzed imino-azaenamine reaction

The enantioselective Br?nsted acid catalyzed addition of methyleneaminopyrrolidine to N-Boc imines has been achieved in the presence of chiral phosphoric acids derived from 3,3'-di(phenanthryl)-H8-BINOL. The corresponding aminohydrazones have been isolated in good yields with enantiomeric excesses up to 90%. [reaction: see text]     

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.     

Asymmetric Brønsted acid catalyzed carbonyl activation--organocatalytic domino electrocyclization-halogenation reaction

A highly efficient Br?nsted acid catalyzed enantioselective Nazarov cyclization-bromination reaction has been developed. The protocol gives access to highly functionalized trans-4,5-substituted 5-bromocyclopentenone derivatives in good yields and with excellent enantioselectivities.     

Direct thioesterification from carboxylic acids and thiols catalyzed by a Brønsted acid

In the presence of a catalytic amount of trifluoromethanesulfonic acid, free carboxylic acids reacted with free thiols directly to afford the corresponding thioesters in high yields.     

Highly efficient asymmetric Mannich reaction of dialkyl α-diazomethylphosphonates with N-carbamoyl imines catalyzed by chiral Brønsted acids

An efficient method involving the first use of chiral phosphoric acids as catalysts in the asymmetric Mannich reaction of dialkyl diazomethylphosphonates and N-carbamoyl imines is developed. With only 0.1 mol % catalyst 1f, the reaction proceeded smoothly and produced the corresponding β-amino-α-diazophosphonate with up to 97% yield and >99% ee.     

Brønsted-acid and Brønsted-base catalyzed Diels-Alder reactions

The enantioselective Diels-Alder reaction is one of the most important reactions for the synthesis of complex molecules. It provides access to chiral six-membered carbocyclic compounds containing up to four stereogenic centers in a single step. Asymmetric catalysis in the Diels-Alder reaction has mainly been realized using chiral Lewis acids. In this perspective, we describe several cases of chiral Br?nsted-acid and Br?nsted-base catalyzed Diels-Alder reactions, providing an overview of this rapidly growing field.     

Enantioselective photocycloaddition mediated by chiral Brønsted acids: asymmetric synthesis of the rocaglamides

Enantioselective syntheses of methyl rocaglate and the related natural products rocaglamide and rocaglaol are outlined. The approach involves enantioselective [3 + 2] photocycloaddition promoted by chiral Br?nsted acids (TADDOLs) to afford an aglain precursor followed by a ketol shift/reduction sequence to the rocaglate core.     

Asymmetric protonation of lithium enolates of alpha-amino acid derivatives with alpha-amino acid-based chiral Brønsted acids

The reaction of lithium enolates of alpha-amino acid derivatives with chiral amides, easily synthesized from L-tert-leucine, gives corresponding optically active unnatural alpha-amino acid derivatives with up to 87% ee.     

Enantioselective synthesis of anti- and syn-homopropargyl alcohols via chiral Brønsted acid catalyzed asymmetric allenylboration reactions

Chiral Br?nsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in highly diastereoselective syntheses of a variety of anti, anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents.     

Asymmetric cross aldol addition of isatins with α,β-unsaturated ketones catalyzed by a bifunctional Brønsted acid–Brønsted base organocatalyst

The asymmetric cross-aldol reaction of isatins with α,β-unsaturated ketones has been developed under catalysis by a Cinchona alkaloid-derivated bifunctional Brønsted acid–Brønsted base catalyst, affording the aldol adducts in moderate to good yields (18–98%) with moderate to good enantioselectivities (30–97%). The noncovalent organo-catalyzed asymmetric cross-aldol reaction displays a broad substrate scope and wide functional-group tolerability, albeit the electronic and steric properties of both reaction partners have considerable and regular effects on the reactivity and stereocontrol.