Remote Sulfonamido Group Enhances Reactivity and Selectivity for Asymmetric Michael Addition of Nitroalkanes to α,β‐Unsaturated Aldehydes

The pyrrolidine–camphorsulfonamide‐based catalyst 1 a catalyzes the enantioselective conjugate addition of nitroalkanes to α,β‐unsaturated aldehydes in the presence of five equivalents of water in iPrOH to give the corresponding chiral Michael adducts in good yields and high enantioselectivities (up to 99 % ee) with a catalyst loading as low as 1 mol %.     

Asymmetric Conjugate Reduction of α,β‐Unsaturated Ketones and Esters with Chiral Rhodium(2,6‐bisoxazolinylphenyl) Catalysts

New asymmetric conjugate reduction of β,β‐disubstituted α,β‐unsaturated ketones and esters was accomplished with alkoxylhydrosilanes in the presence of chiral rhodium(2,6‐bisoxazolinylphenyl) complexes in high yields and high enantioselectivity. (E)‐4‐Phenyl‐3‐penten‐2‐one and (E)‐4‐phenyl‐4‐isopropyl‐3‐penten‐2‐one were readily reduced at 60 °C in 95 % ee and 98 % ee, respectively, by 1 mol % of catalyst loading. (EtO)₂MeSiH proved to be the best hydrogen donor of choice. tert‐Butyl (E)‐β‐methylcinnamate and β‐isopropylcinnamate could also be reduced to the corresponding dihydrocinnamate derivatives up to 98 % ee.     

Asymmetric Conjugate Alkynylation of Cyclic α,β‐Unsaturated Carbonyl Compounds with a Chiral Diene Rhodium Catalyst

Asymmetric conjugate alkynylation of cyclic α,β‐unsaturated carbonyl compounds (ketones, esters, and amides) was realized by use of diphenyl[(triisopropylsilyl)ethynyl]methanol as an alkynylating reagent in the presence of a rhodium catalyst coordinated with a new chiral diene ligand (Fc‐bod; bod=bicyclo[2.2.2]octa‐2,5‐diene, Fc=ferrocenyl) to give high yields of the corresponding β‐alkynyl‐substituted carbonyl compounds with 95–98 % ee.     

Efficient P‐Chiral Biaryl Bisphosphorus Ligands for Palladium‐Catalyzed Asymmetric Hydrogenation

A series of structurally novel P‐chiral biaryl bisphosphorus ligands L1‐L5 (BABIBOPs) are developed, providing high efficiency for the first time in palladium‐catalyzed asymmetric hydrogenation of β‐aryl and β‐alkyl substituted β‐keto esters. With the Pd‐ L3 (iPr‐BABIBOP) catalyst, a series of chiral β‐hydroxyl carboxylic esters are formed in excellent enantioselectivities (up to>99% ee) and yields at catalyst loading as low as 0.01 mol%.     

Magnesium Complexes as Highly Effective Catalysts for Conjugate Cyanation of α,β‐Unsaturated Amides and Ketones

Asymmetric cyanation of trimethylsilyl cyanide (TMSCN) with α,β‐unsaturated amides and ketones, respectively, catalyzed by bifunctional mononuclear 1,1′‐bi‐2‐naphthol (BINOL)–Mg and binuclear bis(prophenol)–Mg catalysts was realized. A series of synthetically important 1,4‐cyano products were obtained with good to high enantioselectivities (up to 97 % ee).     

Efficient Synthesis of β‐Hydroxy‐α‐Amino Acid Derivatives via Direct Catalytic Asymmetric Aldol Reaction of α‐Isothiocyanato Imide with Aldehydes

An easily available and efficient chiral N,N′‐dioxide–nickel(II) complex catalyst has been developed for the direct catalytic asymmetric aldol reaction of α‐isothiocyanato imide with aldehydes which produces the products in morderate to high yields (up to 98 %) with excellent diastereo‐ (up to >99:1 d.r.) and enantioselectivities (up to >99 % ee). A variety of aromatic, heteroaromatic, α,β‐unsaturated, and aliphatic aldehydes were found to be suitable substrates in the presence of 2.5 mol % L ‐proline‐derived N,N′‐dioxide L5 –nickel(II) complex. This process was air‐tolerant and easily manipulated with available reagents. Based on experimental investigations, a possible transition state has been proposed to explain the origin of reactivity and asymmetric inductivity.     

Mechanism of the Asymmetric Hydrogenation of Exocyclic α,β‐Unsaturated Carbonyl Compounds with an Iridium/BiphPhox Catalyst: NMR and DFT Studies

The mechanism of the asymmetric hydrogenation of exocyclic α,β‐unsaturated carbonyl compounds with the (aS)‐Ir/iPr‐BiphPhox catalyst was studied by NMR experiments and DFT computational analyses. Computed optical yields of the asymmetric hydrogenation proceeding by an iridium(I)/iridium(III) mechanism involving a transition state stabilized through two intramolecular hydrogen bonds are in good accordance with the experimental ee values.     

Chiral Nanoparticles/Lewis Acids as Cooperative Catalysts for Asymmetric 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Amides

Cooperative catalysts consisting of chiral Rh/Ag nanoparticles and Sc(OTf)₃ have been developed that catalyze asymmetric 1,4‐addition reactions of arylboronic acids with α,β‐unsaturated amides efficiently. The reaction has been considered one of the most challenging reactions because of the low reactivity of the amide substrates. The new catalysts provide the desired products with outstanding enantioselectivities (>98 % ee) in the presence of low loadings (<0.5 mol %) of the catalyst.     

CeCl3/Sm System Induced Reductive Cleavage of the Se‐Se Bond in Diaryl Diselenides: A Novel Method for the Synthesis of β‐Selenoesters and β‐Selenonitriles

The Se‐Se bond in diselenides was reduced by CeCl₃/Sm system to produce selenolate anions, which react with α,β‐unsaturated esters or α,β‐unsaturated nitriles to afford β‐selenoesters and β‐selenonitriles, respectively.     

Highly Enantioselective Conjugate Additions of Phosphites to α,β‐Unsaturated N‐Acylpyrroles and Imines: A Practical Approach to Enantiomerically Enriched Amino Phosphonates

The first highly enantioselective phosphonylation of α,β‐unsaturated N‐acylpyrroles has been developed. Excellent yields (91–99 %) and enantioselectivities (up to >99 % enantiomeric excess (ee)) were observed for a broad spectrum of both phosphites and N‐acylpyrroles under mild conditions. In particular, when diethyl phosphite was employed to test the scope of the N‐acylpyrroles, almost optically pure products (98 to >99 % ee) were obtained for 20 examples of N‐acylpyrroles. Moreover, optically pure α‐substituted β‐ or γ‐amino phosphonates can be obtained by several simple transformations of the pyrrolyl phosphonates. The versatility of the N‐acylpyrrole moiety makes the phosphorus adducts powerful chiral building blocks that enable the synthesis of various phosphonate‐containing compounds. Finally, the present strategy can also be applied to the asymmetric hydrophosphonylation of N‐acylimines with high enantioselectivities (93 to >99 % ee).     

Iridium‐Catalyzed Enantioselective Allylic Substitution of Unstabilized Enolates Derived from α,β‐Unsaturated Ketones

We report Ir‐catalyzed, enantioselective allylic substitution reactions of unstabilized silyl enolates derived from α,β‐unsaturated ketones. Asymmetric allylic substitution of a variety of allylic carbonates with silyl enolates gave allylated products in 62–94 % yield with 90–98 % ee and >20:1 branched‐to‐linear selectivity. The synthetic utility of this method was illustrated by the short synthesis of an anticancer agent, TEI‐9826.     

Synthesis of Functionalized Indoles with a Trifluoromethyl‐Substituted Stereogenic Tertiary Carbon Atom Through an Enantioselective Friedel–Crafts Alkylation with β‐Trifluoromethyl‐α,β‐enones

Chiral complexes of BINOL‐based ligands with zirconium tert‐butoxide catalyze the Friedel–Crafts alkylation reaction of indoles with β‐trifluoromethyl‐α,β‐unsaturated ketones to give functionalized indoles with an asymmetric tertiary carbon center attached to a trifluoromethyl group. The reaction can be applied to a large number of substituted α‐trifluoromethyl enones and substituted indoles. The expected products were obtained with good yields and ees of up to 99 %.     

A Novel Method for the Synthesis of α,β‐Unsaturated Amides Mediated by Samarium Diiodide

Promoted by Samarium diiodide (SmI₂), α,β‐unsaturated amides were formed from nitrogen anions (formed in situ by the reduction of nitro compounds) and α,β‐unsaturated esters. This reaction contrasts with the conjugate addition between amines and α,β‐unsaturated esters promoted by samarium triiodide (SmI₃) and provides an alternative attractive way to obtain α,β‐unsaturated amides using SmI₂.     

Highly Regio‐ and Enantioselective Synthesis of γ,δ‐Unsaturated Amido Esters by Catalytic Hydrogenation of Conjugated Enamides

An efficient and highly regio‐ and enantioselective catalytic asymmetric hydrogenation of α,γ‐dienamido esters to γ,δ‐unsaturated amido esters has been achieved using Rh/TangPhos as the catalyst. A series of γ,δ‐unsaturated amido acids were furnished in excellent yields with up to 99 % ee. This effective methodology was applied in the asymmetric synthesis of key intermediate of Ramipril, an ACE inhibitor.     

Development of Chiral Spiro P‐N‐S Ligands for Iridium‐Catalyzed Asymmetric Hydrogenation of β‐Alkyl‐β‐Ketoesters

The chiral tridentate spiro P‐N‐S ligands (SpiroSAP) were developed, and their iridium complexes were prepared. Introduction of a 1,3‐dithiane moiety into the ligand resulted in a highly efficient chiral iridium catalyst for asymmetric hydrogenation of β‐alkyl‐β‐ketoesters, producing chiral β‐alkyl‐β‐hydroxyesters with excellent enantioselectivities (95–99.9 % ee) and turnover numbers of up to 355 000.     

Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate‐Addition Reactions of Boron in Water

We have developed Cu^II‐catalyzed enantioselective conjugate‐addition reactions of boron to α,β‐unsaturated carbonyl compounds and α,β,γ,δ‐unsaturated carbonyl compounds in water. In contrast to the previously reported Cu^I catalysis that required organic solvents, chiral Cu^II catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)₂ with chiral ligand L1 ; cat. 2: Cu(OH)₂ and acetic acid with ligand L1 ; and cat. 3: Cu(OAc)₂ with ligand L1 . Whereas cat. 1 is a heterogeneous system, cat. 2 and cat. 3 are homogeneous systems. We tested 27 α,β‐unsaturated carbonyl compounds and an α,β‐unsaturated nitrile compound, including acyclic and cyclic α,β‐unsaturated ketones, acyclic and cyclic β,β‐disubstituted enones, acyclic and cyclic α,β‐unsaturated esters (including their β,β‐disubstituted forms), and acyclic α,β‐unsaturated amides (including their β,β‐disubstituted forms). We found that cat. 2 and cat. 3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat. 1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43 200 h^?1) for an asymmetric conjugate‐addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to α,β,γ,δ‐unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4‐Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic α,β,γ,δ‐unsaturated carbonyl compounds with diboron 2 by using cat. 1, cat. 2, or cat. 3. On the other hand, in the reactions of cyclic α,β,γ,δ‐unsaturated carbonyl compounds with compound 2 , whereas 1,4‐addition products were exclusively obtained by using cat. 2 or cat. 3, 1,6‐addition products were exclusively produced by using cat. 1. Similar unique reactivities and selectivities were also shown in the reactions of cyclic trienones. Finally, the reaction mechanisms of these unique conjugate‐addition reactions in water were investigated and we propose stereochemical models that are supported by X‐ray crystallography and MS (ESI) analysis. Although the role of water has not been completely revealed, water is expected to be effective in the activation of a borylcopper(II) intermediate and a protonation event subsequent to the nucleophilic addition step, thereby leading to overwhelmingly high catalytic turnover.     

Origin of the Enantioselectivity in Organocatalytic Michael Additions of β‐Ketoamides to α,β‐Unsaturated Carbonyls: A Combined Experimental,Spectroscopic and Theoretical Study

The organocatalytic enantioselective conjugate addition of secondary β‐ketoamides to α,β‐unsaturated carbonyl compounds is reported. Use of bifunctional Takemoto’s thiourea catalyst allows enantiocontrol of the reaction leading either to simple Michael adducts or spirocyclic aminals in up to 99 % ee. The origin of the enantioselectivity has been rationalised based on combined DFT calculations and kinetic analysis. This study provides a deeper understanding of the reaction mechanism, which involves a predominant role of the secondary amide proton, and clarifies the complex interactions occurring between substrates and the catalyst.     

Diphenylprolinol Silyl Ether Catalyzed Asymmetric Michael Reaction of Nitroalkanes and β,β‐Disubstituted α,β‐Unsaturated Aldehydes for the Construction of All‐Carbon Quaternary Stereogenic Centers

The asymmetric Michael reaction of nitroalkanes and β,β‐disubstituted α,β‐unsaturated aldehydes was catalyzed by diphenylprolinol silyl ether to afford 1,4‐addition products with an all‐carbon quaternary stereogenic center with excellent enantioselectivity. The reaction is general for β‐substituents such as β‐aryl and β‐alkyl groups, and both nitromethane and nitroethane can be employed. The addition of nitroethane is considered a synthetic equivalent of the asymmetric Michael reaction of ethyl and acetyl substituents by means of radical denitration and Nef reaction, respectively. The short asymmetric synthesis of (S)‐ethosuximide with a quaternary carbon center was accomplished by using the present asymmetric Michael reaction as the key step. The reaction mechanism that involves the E/Z isomerization of α,β‐unsaturated aldehydes, the retro‐Michael reaction, and the different reactivity between nitromethane and nitroethane is discussed.     

Organocatalyzed Cyclopropanation of α‐Substituted α,β‐Unsaturated Aldehydes: Enantioselective Synthesis of Cyclopropanes Bearing a Chiral Quaternary Center

An enantioselective cyclopropanation of α‐substituted α,β‐unsaturated aldehydes with bromomalonate has been successfully developed through a domino Michael/α‐alkylation strategy. The method allows the efficient formation of cyclopropanes bearing a quaternary carbon stereocenter at the α‐position of the aldehydes by using iminium/enamine catalysis and gives a nice extension on the organocatalytic cyclopropanation of bromomalonate and α,β‐unsaturated aldehydes previously reported by other groups. Very good yields (up to 81 %) and enantioselectivities (up to 97 % ee) have been obtained. The optically active cyclopropane derivatives are of high synthetic interest as useful targets for further elaboration into more complex structures.     

Copper‐Catalyzed Asymmetric Synthesis of Tertiary α‐Hydroxy Phosphonic Acid Derivatives with In Situ Generated Nitrosocarbonyl Compounds as the Oxygen Source

α‐Hydroxy phosphonic acids and their derivatives are highly bioactive structural motifs. It is now reported that these compounds can be accessed through the copper‐catalyzed direct α‐oxidation of β‐ketophosphonates using in situ generated nitrosocarbonyl compounds as an electrophilic oxygen source. These reactions proceeded in high yields (up to 95 %) and enantioselectivities (up to >99 % ee) for both cyclic as well as acyclic substrates. This method was also applied for the synthesis of α,β‐dihydroxy phosphonates and β‐amino‐α‐hydroxy phosphonates.