Synthesis of an Enantiocomplementary Catalyst of β‐Isocupreidine (β‐ICD) from Quinine

Compound 20 , a pseudoenantiomer of β‐isocupreidine (β‐ICD), was synthesized from quinine employing a Barton reaction of nitrosyl ester 13 and acid‐catalyzed cyclization of carbinol 18 as key steps. The Baylis–Hillman reaction of benzaldehyde, p‐nitrobenzaldehyde, and hydrocinnamaldehyde with 1,1,1,3,3,3‐hexafluoroisopropyl acrylate (HFIPA) using 20 as a chiral amine catalyst was found to give the corresponding S‐enriched adducts in high optical purity (>91% ee) in contrast to the β‐ICD‐catalyzed reaction which affords R‐enriched adducts. This result suggests that compound 20 can serve as an enantiocomplementary catalyst of β‐ICD in the asymmetric Baylis–Hillman reaction of aldehydes with HFIPA.     

Quinine‐Catalyzed Enantioselective Michael Addition of Diphenyl Phosphite to Nitroolefins: Synthesis of Chiral Precursors of α‐Substituted β‐Aminophosphonates

A quinine‐promoted, enantioselective Michael addition reaction of diphenyl phosphite with nitroalkenes has been developed. This methodology affords a facile access to enantiomerically enriched β‐nitrophosphates, precursors for the preparation of synthetically and biologically useful β‐aminophosphonates.     

Cinchona Alkaloid‐Catalyzed Enantioselective Amination of α,β‐Unsaturated Ketones: An Asymmetric Approach to Δ2‐Pyrazolines

Δ²‐Pyrazolines are of significant medicinal and synthetic interest due to their therapeutic properties and utility in the synthesis of 1,3‐diamines, yet few asymmetric methods exist to prepare them. An unprecedented and highly enantioselective organocatalytic synthesis of 2‐pyrazolines was achieved through an asymmetric conjugate addition catalyzed by 9‐epi‐amino Cinchona alkaloids followed by deprotection‐cyclization, which furnished chiral 2‐pyrazolines in 46–78% yield and 59–91% ee. This bifunctional catalytic methodology thus provides easy access to a considerable range of optically active 3,5‐dialkyl 2‐pyrazolines.     

An Enantioselective Three‐Component Sulfa‐Michael/Aldol Cascade Reaction and its Application to the Synthesis of Thioaryl Substituted (−)‐Bestatin Derivatives

An efficient catalytic asymmetric three‐component sulfa‐Michael/aldol cascade reaction has been developed using a chiral multi‐functional catalyst. This reaction provided facile access to γ‐sulfur‐β‐nitro‐α‐hydroxy esters bearing three consecutive linear stereocenters in high yields (up to 97%) with excellent diastereo‐ (up to >97:3 dr) and enantioselectivities (>99% ee). These compounds were readily converted into 2‐nitroallylic alcohols and potentially bioactive γ‐sulfur‐β‐amino‐α‐hydroxy esters, which could be further used for the synthesis of Bestatin derivatives.

     

Enantioselective Organocatalytic Rearrangement of α‐Acyloxy‐ β‐keto Sulfides to α‐Acyloxy Thioesters

The first highly enantioselective organocatalytic rearrangement of α‐acyloxy‐β‐keto sulfides to α‐acyloxy thioesters has been developed which provides a number of important synthetic building blocks in high yield and with excellent enantioselectivities (ee: up to 92%).     

Synthesis of 2‐Aryl‐Substituted Indole‐3‐acetic Acid Derivatives via Intramolecular Imino‐Stetter Reaction of Aldimines with Cyanide

A general method to generate umpolung of aldimines with cyanide was developed via the addition of cyanide to aldimines followed by a proton transfer from the carbon atom to the nitrogen atom in the resulting cyanide adducts. This novel method was successfully applied to the first imino‐Stetter reaction of aldimines obtained from 2‐aminocinnamic acid derivatives and aromatic aldehydes with cyanide, affording 2‐aryl‐substituted indole‐3‐acetic acid derivatives. Furthermore, the usefulness of this method was successfully demonstrated by the synthesis of an FPTase inhibitor, one of the biologically important 2‐arylindole‐3‐acetic acid derivatives.

     

Efficient Oxidative Cleavage of Tetrahydrofuran‐2‐methanols to γ‐Lactones by a 2‐Iodobenzamide Catalyst in Combination with Oxone®

An environmentally friendly oxidative cleavage of tetrahydrofuran‐2‐methanols to the corresponding γ‐lactones using a catalytic amount of 2‐iodo‐N‐isopropylbenzamide has been developed. The reaction of various tetrahydrofuran‐2‐methanols with the catalyst in the presence of Oxone^® (2 KHSO₅⋅KHSO₄⋅K₂SO₄) as a co‐oxidant in DMF at room temperature successfully affords the corresponding lactones in good to high yields, and recovery of the catalyst is readily accomplished using a reductive work‐up. This method is notable because it enables the transformation of tetrahydrofuran‐2‐methanols to γ‐lactones under mild conditions without the use of any toxic heavy metals.

     

Catalysis by β‐Cyclodextrin Hydrate – Synthesis of 2,2‐Disubstituted 2H‐Chromenes in Aqueous Medium

A cost‐effective, operationally simple and eco‐compatible protocol for the one‐pot synthesis of photochromic pyrans by the reaction of propargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous medium has been developed using β‐cyclodextrin hydrate as an efficient, recyclable and stable catalyst. This is the first report where β‐cyclodextrin hydrate acted as a catalyst for an organic transformation but β‐cyclodextrin alone failed.

     

Oxygen‐Involved Oxidative Deacetylation of α‐Substituted β‐Acetyl Amides – Synthesis of α‐Keto Amides

α‐Substituted β‐acetyl amides could undergo C C bond cleavage to form α‐keto amides when treated with copper(II) chloride (CuCl₂) and boron trifluoride diethyl etherate (BF₃⋅OEt₂) under an oxygen atmosphere. The yield can be increased by the addition of tert‐butyl hydroperoxide which alone can also effect the reaction. The reaction provides a new protocol for the synthesis of α‐keto amides.

     

Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

An efficient, selective and recoverable catalytic system for ligand‐free aqueous Heck reactions using hydroxypropylated cyclodextrins (HPCDs) and palladium on calcium carbonate (Pd/CaCO₃) is highlighted. Remarkably, stereo‐ and chemoselectivities could be tuned by the cavity size of cyclodextrins, exploiting the relevance of host‐guest interactions. UV‐Vis experiments have led to strong evidence concerning an interplay between Pd(II) and α‐HPCD, possibly ascribed to a reduction/stabilization effect of CDs. Unexpectedly, hydroarylation was the favored pathway with acrylonitrile which provided access to 3‐phenylpropionitrile derivatives without usual hydride donors. Finally, determination of soluble Pd(0/II) via AAS enabled the definition of a predominant homogeneous mechanism in which TONs over 5000 were observed.     

Using Conveniently Designed α‐Amino Ketones in Michael Reactions under Iminium Catalysis: Enantioselective Synthesis of γ‐Lactams and γ‐Amino‐δ‐keto Esters

The behaviour of aminoacetophenones as Michael donors in catalytic enantioselective Michael reactions with α,β‐unsaturated aldehydes under iminium activation has been studied. These compounds react with each other in the presence of catalytic amounts of a chiral secondary amine through a Michael/hemiaminal formation cascade process which proceeds with high yields and enantiocontrol. Elaboration of these adducts by oxidation allows the easy access to chiral disubstituted γ‐lactams and other synthetically useful chiral building blocks such as γ‐amino‐δ‐keto esters or β‐substituted δ‐oxoamides are accessible from the obtained adducts by simple transformations.     

Kinetic Resolution of Aliphatic β‐Amino Acid Amides by β‐Aminopeptidases

Access to enantiopure β‐amino acids : β‐Aminopeptidases are hydrolases that possess the unique ability to cleave N‐terminal β‐amino acids from peptides and amides. Hydrolysis of racemic β‐amino acid amides catalyzed by these enzymes displays enantioselectivity with strong preference for substrates with the L ‐configuration, and gives access to various aliphatic β‐amino acids of high enantiopurity.

     

Organocatalysis in Enantioselective α‐Functionalization of 2‐Cyanoacetates

Recent progress in asymmetric organocatalysis has led to the development of several asymmetric transformations that employ various substrates. Among these, cyanoacetates have emerged as excellent nucleophiles in conjugate addition, alkylation, Mannich and α‐heterofunctionalization reactions. In this review we discuss the enantioselective functionalization of 2‐cyanoacetates through organocatalytic reactions.

     

Organocatalytic Reactions of Indoles with Quinone Imine Ketals: An Alternative Metal‐Free Approach to Bioactive meta‐Indolylanilines

An organocatalytic metal‐free strategy has been established for the synthesis of pharmaceutically relevant meta‐indolylanilines in generally excellent yields (up to 99 %). This strategy took advantage of the reaction of indoles and quinone imine ketals (QIKs) in the presence of racemic phosphoric acid, which proceeded via a 1,4‐addition/alcohol elimination reaction sequence. The control experiment demonstrated that the dual hydrogen‐bonding activation mode of the catalyst to the substrates played a crucial role in the reaction. This protocol provides a metal‐free and step‐economical approach to meta‐anilines bearing either 3‐indolyl or 2‐indolyl moiety, which is of high value for the synthesis of compounds with potential bioactivities.

     

Gold(I)‐Catalyzed Carboaminations of Allenes by N‐Allyltetrahydro‐β‐carbolines: An Experimental and Theoretical Study

N‐Allyltetrahydro‐β‐carbolines bearing a pendant allene undergo unprecedented gold(I)‐catalyzed cyclizations proceeding with an allyl migration from the nitrogen to the allene moiety. The initial product of the gold‐catalyzed cyclization evolves either via isomerization or Cope rearrangement, leading to different scaffolds. Density function theory (DFT) calculations established that the allyl migration occurs in an asynchronous suprafacial manner.

     

A Recyclable Organocascade Reaction System: Stereoselective Precipitation of Optically Active cis‐δ‐Lactols with Quaternary Stereocenters during the Michael–Hemiacetalization Reaction

A cascade Michael–hemiacetalization reaction between β‐substituted β‐nitroethanols and α,β‐unsaturated aldehydes is described, which provides a convenient and efficient synthesis for cis‐δ‐lactols with quaternary stereocenters in moderate yields with excellent enantioselectivity. Based on the selective precipitation of cis‐δ‐lactols, which were isolated by filtration, the catalytic system in the filtrate can be reused directly and recycled for eight times without any obvious deterioration in enantioselectivity.     

Organocatalytic Enantioselective Aziridination of α‐Substituted α,β‐Unsaturated Aldehydes: Asymmetric Synthesis of Terminal Aziridines

The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2).     

Silver‐Catalyzed Intramolecular C‐2 Selective Acylation of Indoles with Aldehydes: An Atom‐Economical Entry to Indole‐Indolone Scaffolds

A direct annulation reaction of N‐(2‐formylaryl)indoles has been developed, which can provide a new entry to biologically and medicinally important indole‐indolone scaffolds via a silver‐catalyzed direct oxidative coupling between aldehyde C H and sp² C H bonds for the first time. Remarkably, this strategy displayed excellent functional group compatibilities, thereby suggesting its wide potential for applications in developing and synthesizing new drug‐like compounds containing indole‐indolone frameworks.