Enantiodivergent Reaction of Ketimines with Malononitriles Using Single Cinchona Alkaloid Sulfonamide Catalysts

Chiral Phosphoric Acid-Catalyzed Enantioselective Synthesis of 2,2-Disubstituted 2,3-Dihydro-4-quinolones from Isatins and 2'-Aminoacetophenones

Herein, we present the enantioselective synthesis of 2,3-dihydro-4-quinolones bearing chiral tetrasubstituted carbons from isatins and 2'-aminoacetophenones. The transformation is mediated by a chiral phosphoric acid catalyst and proceeds via an in situ generated ketimine and subsequent enantioselective intramolecular cyclization. The methodology features a broad scope and functional group tolerance with yields and enantioselectivities of up to 99% and 98% ee. Detailed density functional theory (DFT) calculations support the proposed reaction mechanism and the origin of asymmetric induction.

Synthesis of tricarbonylated propargylamine and conversion to 2,5-disubstituted oxazole-4-carboxylates

The N,O-acetal derived from diethyl mesoxalate (DEMO) undergoes elimination of acetic acid upon treatment with a base, leading to the formation of N-acylimine in situ. Lithium acetylide readily attacks the imino group to afford N,1,1-tricarbonylated propargylamines. When the resulting propargylamine reacts with butyllithium, ring closure occurs between the ethynyl and carbamoyl groups, yielding 2,5-disubstituted oxazole-4-carboxylates. This cyclization also occurs when the propargylamine is heated with ammonium acetate, resulting in double activation.

Asymmetric Conjugate Addition of Phosphine Sulfides to α-Substituted β-Nitroacrylates Using Cinchona Alkaloid Amide Catalysts

Chiral phosphine-containing amino acids are useful motifs in pharmaceutical compounds. In this study, we developed the asymmetric conjugate addition of phosphine sulfides with α-substituted β-nitroacrylates to synthesize phosphine-containing amino acid precursors with chiral tetrasubstituted carbon centers. This method showed a wide substrate scope, and the obtained products were converted into various chiral compounds. The origin of the enantioselectivity was clarified by computational analysis.

Asymmetric Cascade Dearomatization-Cyclization Reaction of Tryptamines with β,γ-Alkynyl-α-imino Esters: Access to Hexahydropyrrolo[2,3-b]indole-Containing Tetrasubstituted α-Amino Allenoates

An organocatalytic enantio- and diastereoselective synthesis of hexahydropyrrolo[2,3-b]indole-containing tetrasubstituted α-amino allenoates, exhibiting both axial and central chirality, has been accomplished via cascade dearomatization-cyclization reaction. The γ-addition to β,γ-alkynyl-α-imino esters provides a library of densely substituted highly enantioenriched allenes in high yields and excellent stereoselectivities. In addition, the scope of this methodology has been extended to tryptophol as well. A scale-up reaction and synthetic transformations of the products were performed to demonstrate the practical usefulness of this approach.

Copper-Catalyzed Direct Asymmetric Vinylogous Mannich Reaction between β,γ-Alkynyl-α-ketimino Esters and β,γ-Unsaturated N-Acylpyrazoles

We report a Cu(I)-Ph-BPE-catalyzed asymmetric vinylogous Mannich reaction of β,γ-alkynyl-α-ketimino esters with β,γ-unsaturated N-acylpyrazoles. In this process, the Cu(I)-Ph-BPE catalyst activates the β,γ-alkynyl-α-ketimino ester through N,O-coordination, enabling the subsequent nucleophilic addition of a dienolate generated from the β,γ-unsaturated N-acylpyrazole via α-position deprotonation with a catalytic amount of tertiary amine. The reactions gave useful products with very high enantioselectivities. A broad range of substrates with various substituents are tolerated in this reaction. The versatility of this method was demonstrated by a gram-scale reaction, and subsequent elaboration of the Mannich adducts was also provided.

Organocatalytic regio- and enantioselective C1-arylation of β,γ-alkynyl-α-imino esters with pyrrolo[2,1-a]isoquinolines

We herein report regio- and enantioselective arylation of β,γ-alkynyl-α-imino esters with pyrroloisoquinolines. Using chiral phosphoric acid catalysts, a wide range of novel axially chiral tetrasubstituted α-amino allenoates were accessed in good yields with excellent enantioselectivities. Notably, this transformation occurred preferentially at the sterically more hindered C1-position of pyrroloisoquinolines. The potential scalability and late-stage functionalization demonstrated the utility of the current protocol.

Scalable Preparation of the Masked Acyl Cyanide TBS-MAC

This paper describes the three-step synthesis of TBS-MAC, a masked acyl cyanide (MAC) and a versatile one-carbon oxidation state three synthon. We have developed a scalable and detailed synthesis that involves: (1) acetylation of malononitrile to form the sodium enolate, (2) protonation of the enolate to form acetylmalononitrile, and (3) epoxidation of the enol, rearrangement to an unstable alcohol, and TBS-protection to form the title compound. Both the sodium enolate and acetylmalononitrile are bench-stable precursors to the intermediate hydroxymalononitrile, which can be converted to other MAC reagents beyond TBS by varying the protecting group (Ac, MOM, EE, etc.).

Direct Catalytic Enantioselective Reaction of α-Isocyanoacetonitriles with Ketimines Using Cinchona Alkaloid Amide-Cu(II) Catalysts

The first enantioselective reaction of α-isocyanoacetonitriles was developed. The reaction of various α-isocyanoacetonitriles with ketimines using cinchona alkaloid amide-Cu(II) catalysts afforded imidazolines with consecutive tetrasubstituted stereogenic carbon centers in good yields and high diastereo- and enantioselectivities. The stereoselectivity of the reaction is explained on the basis of the control experiment and density functional theory (DFT) calculations. The products were subsequently converted into chiral compounds. This process highlights the possible use of α-isocyanoacetonitriles for asymmetric and organic syntheses.

Rapid Construction of Tricyclic Furanobenzodihydropyrans by Asymmetric Tandem Reaction

A process based on the organocatalyzed Mannich/cycloketalization/transesterification tandem reaction of 1-(2-hydroxyaryl)-1,3-diketones and β,γ-alkynyl α-imino esters has been developed, delivering a variety of tricyclic furanobenzodihydropyrans with excellent results (up to 99% yield, 99% ee, and >19:1 dr).

Synthesis of α-Quaternary β-Lactams via Copper-Catalyzed Enantioconvergent Radical C(sp3 )-C(sp2 ) Cross-Coupling with Organoboronate Esters

The copper-catalyzed enantioconvergent radical C(sp³ )-C(sp² ) cross-coupling of tertiary α-bromo-β-lactams with organoboronate esters could provide the synthetically valuable α-quaternary β-lactams. The challenge arises mainly from the construction of sterically congested quaternary stereocenters between the tertiary alkyl radicals and chiral copper(II) species. Herein, we describe our success in achieving such transformations through the utilization of a copper/hemilabile N,N,N-ligand catalyst to forge the sterically congested chiral C(sp³ )-C(sp² ) bond via a single-electron reduction/transmetalation/bond formation catalytic cycle. The synthetic potential of this approach is shown in the straightforward conversion of the corresponding products into many valuable building blocks. We hope that the developed catalytic cycle would open up new vistas for more enantioconvergent cross-coupling reactions.

Enantioselective reaction of N-cyano imines: decarboxylative Mannich-type reaction with malonic acid half thioesters

The enantioselective reaction of imines bearing a cyano group as an activating group with malonic acid half thioesters gave chiral cyanamide derivatives with high enantioselectivity. The density functional theory (DFT) calculation clarified the stereochemical outcome and importance of the N-cyano group for imines.

Enantioselective Pictet-Spengler Reaction of Acyclic α-Ketoesters Using Chiral Imidazoline-Phosphoric Acid Catalysts

The first enantioselective Pictet-Spengler reaction of acyclic α-ketoesters with tryptamines has been developed. Excellent yields and enantioselectivity were obtained for the reaction using chiral imidazoline-phosphoric acid catalysts. Density functional theory calculations suggested possible transition states that explain the origin of chiral induction. This process provides an efficient route for the synthesis of tetrahydro-β-carboline derivatives.

Organocatalytic asymmetric synthesis of quaternary α-isoxazole–α-alkynyl amino acid derivatives

Chiral phosphoric acid catalyzed enantioselective addition of 5-amino-isoxazoles with β,γ-alkynyl-α-ketimino esters provided good yields and excellent enantioselectivities.