En route to an efficient catalytic asymmetric synthesis of AS-3201

Stereoselective Synthesis of Less Accessible α-Tertiary Amino Ketimines via Electrophilic Amination of α-Branched N-tert-Butanesulfinyl Ketimines

A stereocontrolled electrophilic amination of α-branched N-tert-butanesulfinyl ketimines was developed to construct α-aminoketone derivatives containing less accessible α-tetrasubstituted stereocenters. Stereospecific α-deprotonation of ketimines with potassium tert-butoxide gave stereodefined metalloenamine intermediates that could act as nucleophiles to attack azodicarboxylic derivatives, affording α-aminated products in high yields with excellent stereoselectivities.

Enantioselective and Chemoselective Phosphine Oxide-catalyzed Aldol Reactions of N-Unprotected Cyclic Carboxyimides

Asymmetric catalytic transformations of N-unprotected cyclic carboxyimides such as succinimides, hydantoins, oxazolidinediones, and glitazones, is a powerful way of directly accessing variety of biologically valuable chiral compounds. Herein, a bis(trichlorosilyl) nucleophilic intermediate formed from cyclic carboxyimides was reacted with aldehydes via (S)-SEGPHOS dioxide (SEGPHOSO), proceeding the aldol reaction in highly enantioselective fashion through a cyclic transition state. Furthermore, N-unprotected carboxyimides were chemoselectively activated, even in the presence of N-alkylated carboxyimides, to undergo stereoselective and chemoselective aldol reactions via in situ silicon tetrachloride activation. The functionalized cyclic carboxyimides is readily derived to the several synthetic units derivatization to various chiral building blocks without unnecessary protection/deprotection steps.

Crystallization-Enabled Henry Reactions: Stereoconvergent Construction of Fully Substituted [N]-Asymmetric Centers

Tetrasubstituted stereogenic carbon centers bearing a nitrogen substituent represent important motifs in medicinal chemistry and natural products; therefore, the development of efficient methods for the stereoselective synthesis of this class of compounds continues to be an important problem. This article describes stereoconvergent Henry reactions of γ,γ-disubstituted nitroalkanes to deliver highly functionalized building blocks containing up to five contiguous stereogenic centers including a fully substituted [N]-asymmetric center. Henry reactions of higher order nitroalkanes are often characterized by their reversibility and minimal accompanying thermodynamic stereocontrol. In contrast, mechanistic studies for the present case suggest a scenario in which reversibility is productively leveraged through crystallization-based stereocontrol, thereby enabling the efficient sequential π-additions of readily accessible starting materials to assemble complex acyclic stereoarrays.

Synthesis of Acyl Hydrazides via a Radical Chemistry of Azocarboxylic tert-Butyl Esters

A new chemistry of azo compounds, that is, addition of free radicals generated in situ to access various acyl hydrazides, has been developed. The protocol provides a novel strategy for the synthesis of valuable acyl hydrazides. The transformation features mild reaction conditions, good tolerance of functional groups, and a broad substrate scope. In view of the importance of acyl hydrazides in functional materials and medicinal chemistry, this approach would find broad applications.

Enantioselective amination of 4-alkylisoquinoline-1,3(2H,4H)-dione derivatives

A mild and efficient enantioselective amination of 4-alkylisoquinoline-1,3(2H,4H)-dione derivatives was established, which is compatible with a broad range of substrates and delivers the final products in excellent yields (up to 99%) and ee values (up to 99%) with low catalyst loading (down to 1 mol%). The synthetic potential of this methodology was also demonstrated in the gram scale level.

Asymmetric catalysis in direct nitromethane-free Henry reactions

This review summarizes the current state and applications of catalytic Henry reactions involving complex nitroalkanes coupling with various carbonyl compounds to generate chiral β-nitro alcohol scaffolds with four adjacent stereogenic centers.

Enantioselective synthesis of quaternary 3,4-dihydroisoquinolinones via Heck carbonylation reactions: development and application to the synthesis of Minalrestat analogues

Minalrestat and its analogues represent structurally novel aldose reductase inhibitors, and the asymmetric synthesis of such pharmaceutically privileged molecules has not been reported yet. We have developed a palladium-catalyzed enantioselective intramolecular carbonylative Heck reaction by using formate esters as the source of CO, which represents the first enantioselective synthesis of quaternary 3,4-dihydroisoquinolines. The reaction provides a facile and efficient method for the synthesis of enantiopure nitrogen-containing heterocyclic compounds bearing an all-carbon quaternary stereocenter. The reaction has been successfully applied to the first asymmetric synthesis of Minalrestat analogues.

Application of dialkyl azodicarboxylate frameworks featuring multi-functional properties

The application of dialkyl azodicarboxylates as versatile reagents in Mitsunobu, oxidation, electrophilic, amination and carbonylation reactions is reviewed.

Direct catalytic enantioselective amination of ketones for the formation of tri- and tetrasubstituted stereocenters

Herein, we report a Zn-ProPhenol catalyzed direct asymmetric amination reaction of unactivated aryl and vinyl ketones using di-tert-butyl azodicarboxylate as a cheap and practical electrophilic nitrogen source. Importantly, this methodology works with both α-branched and unbranched ketones for the construction of tri- and tetrasubstituted N-containing stereocenters. The reaction can be run at gram-scale with low catalyst loadings and features a recoverable and reusable ligand. Finally, the enantioenriched hydrazine products can be readily converted into versatile building blocks such as α-amino carbonyl compounds and β-amino alcohols.

Two-Step Synthesis of 3,4-Dihydropyrrolopyrazinones from Ketones and Piperazin-2-ones

An expedient two-step synthesis of 3,4-dihydropyrrolopyrazinones has been achieved via a Vilsmeier-Haack reaction of ketones, followed by an annulation of the corresponding chloroaldehydes with commercially available piperazin-2-ones. A variety of cyclic and acyclic ketones and piperazin-2-ones participated in this two-step chemistry, affording the desired 3,4-dihydropyrrolopyrazinones in up to 78% yield.

Copper-catalyzed carbonylation of anilines by diisopropyl azodicarboxylate for the synthesis of carbamates

Herein, a simple Cu-catalyzed system for the synthesis of carbamates has been developed using anilines with diisopropyl azodicarboxylate as a carbonyl source under solvent-free conditions.

Recyclable BINOL–quinine–squaramide as a highly efficient organocatalyst for α-amination of 1,3-dicarbonyl compounds and α-cyanoacetates

An efficient organocatalytic asymmetric α-amination of 1,3-dicarbonyl and α-cyanoacetates compounds towards chiral α-amino acid precursors is reported.

Recent advances in asymmetric organocatalysis mediated by bifunctional amine–thioureas bearing multiple hydrogen-bonding donors

Recent progress in asymmetric organocatalysis, focusing on fine-tunable amine–thiourea catalysis, is described. Design of novel bifunctional amine–thiourea organocatalysts bearing multiple hydrogen-bonding donors and their applications in asymmetric C–C, C–N, and C–S bond-forming reactions under mild conditions are discussed.

Asymmetric enamine catalysis with β-ketoesters by chiral primary amine: divergent stereocontrol modes

α-Branched ketones remain a challenging type of substrates in aminocatalysis due to their congested structures as well as the associated difficulties in controlling chemo- and stereoselectivity. In this work, we have explored asymmetric aminocatalysis with α-substituted β-ketoesters. A simple chiral primary amine catalyst was identified to enable unprecedentedly effective catalysis of β-ketoesters in α-hydrazination and Robinson annulation reaction with good yields and high enantioselectivities. Stoichiometric experiments with preformed enamine ester intermediates revealed their enamine-catalytic nature as well as the critical roles of acidic additives in facilitating catalytic turnovers and in tuning the chemo- and stereoselectivity. With the identical catalytic system, the two reactions demonstrated opposite chiral inductions in terms of the absolute configurations of the newly formed stereogenic centers. Investigations into this intriguing issue by DFT have revealed divergent stereocontrol modes. For α-hydrazination, H-bonding-directed facial attack determines the stereoselectivity, whereas a steric model is applied to the Robinson annulation where dual activations of both β-ketoester and vinyl ketone/aldehyde are involved.

Photoorganocatalytic hydroacylation of dialkyl azodicarboxylates by utilising activated ketones as photocatalysts

A fast and efficient visible-light metal-free hydroacylation of dialkyl azodicarboxylates is described. Among a variety of activated ketones, phenyl glyoxylic acid and its ethyl ester were identified as suitable photoorganocatalysts. A range of aliphatic and aromatic aldehydes were employed, thus leading to products in high to excellent yields.

Total syntheses of (-)-hanishin, (-)-longamide B, and (-)-longamide B methyl ester via a novel preparation of N-substituted pyrrole-2-carboxylates [corrected]

A novel preparation of N-substituted pyrrole-2-carboxylates has been developed based upon 1,3-dipolar cycloaddition and a conventional hydrogenolysis. By using this method as the key step, total syntheses of natural alkaloids (-)-hanishin, (-)-longamide [corrected] B, and (-)-longamide [corrected] B methyl ester were accomplished in the highest overall yields, respectively.