Asymmetric Wacker-Type Oxyallenylation and Azaallenylation of Cyclic Alkenes

Palladium-catalyzed three-component carboetherification of cyclic alkenes proceeded to give trans adducts exclusively with excellent enantioselectivity through a Wacker-type pathway. The reaction is also applicable to other oxygen nucleophiles, such as water, phenols, and carboxylic acids, as well as some electron-poor aryl amines.     

Asymmetric Wacker‐Type Oxyallenylation and Azaallenylation of Cyclic Alkenes

Palladium‐catalyzed three‐component carboetherification of cyclic alkenes proceeded to give trans adducts exclusively with excellent enantioselectivity through a Wacker‐type pathway. The reaction is also applicable to other oxygen nucleophiles, such as water, phenols, and carboxylic acids, as well as some electron‐poor aryl amines.     

Rationally designed 4-phenoxy substituted prolinamide phenols organocatalyst for the direct aldol reaction in water

A rationally designed 4-phenoxy substituted prolinamide phenols as an efficient hydrophobic organocatalyst for direct asymmetric aldol reaction in water has been developed. High yield (up to 99%), diastereoselectivity (up to 99:1), and enantioselectivity (up to 97%) were obtained under optimal condition. The influence of substituent groups on the reactivity of catalysts was studied in detail.     

Organocatalytic Asymmetric Addition of Naphthols and Electron‐Rich Phenols to Isatin‐Derived Ketimines: Highly Enantioselective Construction of Tetrasubstituted Stereocenters

A quinine‐derived thiourea organocatalyst promoted the highly enantioselective addition of naphthols and activated phenols to ketimines derived from isatins. The reaction afforded chiral 3‐amino‐2‐oxindoles with a quaternary stereocenter in high yields (up to 99 %) with excellent enantioselectivity (up to 99 % ee). To the best of our knowledge, this transformation is the first highly enantioselective addition of naphthols to ketimines.     

Enantioselective Palladium‐Catalyzed Insertion of α‐Aryl‐α‐diazoacetates into the OH Bonds of Phenols

A palladium‐catalyzed asymmetric O? H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of α‐aryl‐α‐diazoacetates into the O? H bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium‐catalyzed asymmetric O? H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active α‐aryl‐α‐aryloxyacetates.     

Enantioselective Palladium‐Catalyzed Insertion of α‐Aryl‐α‐diazoacetates into the O?H Bonds of Phenols

A palladium‐catalyzed asymmetric O H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of α‐aryl‐α‐diazoacetates into the O H bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium‐catalyzed asymmetric O H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active α‐aryl‐α‐aryloxyacetates.     

Imidazolium-tagged ferrocenyl diphosphanes in allylic substitution with heteroatom nucleophiles

Imidazolium-tagged ferrocenyl diphosphanes are useful ligands in palladium-catalyzed allylic substitutions with heteroatom nucleophiles. Substitution with phthalimide proceeds with high enantioselectivity (up to 92% ee) in various ionic liquids. Reaction with p-cresol as nucleophile affords allylation product in up to 62% ee, while using tolylsulfinate as a nucleophile gives a product with very little or no enantioselectivity. Under these reaction conditions, catalyst recyclability is challenging, and decrease in activity as well as enantioselectivity was observed.     

Diastereoselective Synthesis of Benzoxanthenones

An oxidative catalytic vanadium(V) system was developed to access the naturally nonabundant diastereomers of carpanone from the corresponding alkenyl phenol monomer in one pot by tandem oxidation, oxidative coupling, and 4+2 cyclization. This system was applied to the synthesis of two other analogues of carpanone. Mild oxidizing silver salts were used as the terminal oxidant to minimize background oxidation which produces the natural diastereomer of carpanone. Further, the first examples of enantioselective oxidative benzoxanthenone formation are reported. Solvent polarity has a strong effect on enantioselectivity, consistent with a mechanism involving binding of vanadium Schiff base catalysts to the alcoholic moiety of the alkenyl phenols during the cyclization step.     

Enantioselectivity of Photochemical Reactions within Polymer Microcapsules

Polymer microcapsule was employed as a reactionmedium to achieve enantioselectivity in photochemical reduction of phenyl cyclohexyl ketone and photoelectrocycliztion of tropolone methyl ether under the influence of various chiral inductors.In all cases,low but evident enantioselectivity was observed.The poor enantioselectivity is probably due to the facts that not all the capsules include simultaneously both the chiral inductor and the reactant molecules,and the wall of the microcapsule is not rigid enough to hold the reactant and the chiral inductor molecules in close contact.     

Enantioselective Reactions of 2‐Sulfonylalkyl Phenols with Allenic Esters: Dynamic Kinetic Resolution and [4+2] Cycloaddition Involving ortho‐Quinone Methide Intermediates

We report herein a dynamic kinetic resolution (DKR) involving ortho ‐quinone methide (o ‐QM) intermediates. In the presence of Et₃N and the cinchonine‐derived nucleophilic catalyst D , the DKR of 2‐sulfonylalkyl phenols with allenic esters afforded chiral benzylic sulfones in 57–79 % yield with good to excellent enantioselectivity (85–95 % ee ). Furthermore, with 2‐(tosylmethyl)sesamols or 2‐(tosylmethyl)naphthols, from which stable o ‐QM substrates can be generated, a formal [4+2] cycloaddition delivered 4‐aryl‐ or alkyl‐substituted chromans with excellent enantioselectivity (88–97 % ee ).     

Recent developments in the enantioselective synthesis of polyfunctionalized pyran and chromene derivatives

Recent developments in the synthesis of 4H- and 2H-pyrans as well as structurally related chromene derivatives that have enabled the enantioselective synthesis of these scaffolds have been surveyed. The role of chiral catalysts in orienting initial reactions of active methylenes, methines and methyl ketones, to unsaturated ketones and nitriles in multi-component reactions or Friedel–Craft alkylations of phenols is discussed to show their involvement in transition states leading to end products. Chromene synthesis via [4+2] cycloadditions, [3+3] and [4+2] annulations as well as ring opening and recyclization leading to high enantio- and diasteroselectivity is also demonstrated. The enantioselectivity in such catalytic asymmetric reactions despite starting with non-chiral starting materials is discussed. On the other hand, in surveying ring opening and recyclization, the starting materials are chiral and the chiral center was not part of the reaction leading to the final product.     

N-Picolinamides as ligands in Ullman type C–O coupling reactions

Copper-catalyzed modified Ullmann coupling reactions creating C–O bonds, including diaryl ethers or phenols, are vital to organic synthesis. Synthesized N-phenyl-2-pyridinecarboxamide and its derivatives were used as ligands in conjunction with catalytic copper sources in the formation of various diaryl ethers and phenols. Various aryl and heteroaryl halides with electron donating and withdrawing groups were reacted with various phenols under mild reaction conditions providing moderate to excellent yields.     

Effect of microwave heating in the asymmetric addition of dimethylzinc to aldehydes

Microwave-heated enantioselective additions of dimethylzinc to various aldehydes are reported. Dramatically reduced reaction times and lower catalyst loadings (5%), compared with conventionally used conditions, can be achieved, with excellent yields and just small loss of enantioselectivity (up to 83% enantioselectivity is achieved). In the reaction with aliphatic aldehydes the same enantioselectivity has been achieved for microwave-heated and conventional room temperature conditions.     

新轴手性N,N-Dioxide Biscarbolin衍生物催化酮亚胺的不对称硅氢化反应

以L-色氨酸为原料合成了5个伯酰胺结构的轴手性双咔啉N—O催化剂N2,N2'-二氧-9,9'-二甲基-3,3'-取代甲酰胺-β-双咔啉(4A~4E),并用于不对称催化酮亚胺的还原反应.结果表明,催化剂的催化转化率较高(80%~98%),立体选择性(e.e.值)较好,其中催化剂N2,N2'-二氧-9,9'-二甲基-3,3'-环己基甲酰胺-β-双咔啉(4B)的催化转化率达到了98%,e.e.值达68%.     

Asymmetric organocatalyzed Michael addition of aldehydes to β-nitrostyrene in ionic liquids

The addition of aliphatic aldehydes to β-nitrostyrene, catalyzed by proline-derived organocatalysts, proceeded well in various ionic liquids. Products were obtained in high yields and syn/anti diastereoselectivity. However, the enantioselectivity was only mediocre, even though some analogous reactions in organic solvents were highly enantioselective. We also evaluated the temperature effect on the diastereoselectivity as well as on the enantioselectivity of the Michael addition.     

Impact of amines as co-modifiers on the enantioseparation of various amino acid derivatives on a tert-butyl carbamoylated quinine-based chiral stationary phase

A tert-butyl carbamoylated quinine-based chiral stationary phase (CSP) for direct enantiomer separation of various natural and unnatural amino acid derivatives was studied. The influence of functional groups in the amino acid side chains upon the enantioseparation is discussed with the aim of realizing contributions to their overall chiral recognition. The effects of various amines as co-modifiers upon retention and overall enantioselectivity of amino acid derivatives in polar organic solvents was systematically investigated. In general, retention times decreased with increasing amine concentrations without a distinct alteration of enantioselectivity. All analytes were rapidly resolved on the CSP with the methanol-based mobile phase containing 87 mM acetic acid and 7 mM triethylamine.     

Enantioselective reaction of alpha-lithiated dithioacetals using chiral bis(oxazoline)s: new chiral formyl anion equivalents

The enantioselective reaction of various alpha-lithiated dithioacetals with aldehydes or a ketone in the presence of bis(oxazoline)s was examined. Among them, unsymmetrical dithioacetals were found to be the best choice for attaining high enantioselectivity. The reaction of lithiated tert-butylthio(2-pyridylthio)methane with aldehydes proceeded with good diastereoselectivity as well as with good enantioselectivity. The enantioselective reaction was shown to proceed through dynamic thermodynamic resolution. Mercury(II) chloride effected hydrolysis of the dithioacetal moiety of the products to 2-hydroxyaldehydes, which were directly reduced to give the optically active 1,2-diols.     

Investigation into the determination of phenols extracted from automobile exhaust gases

A method is described in which phenols extracted from the condensate of automobile exhaust gases are determined directly by GLC. The quantities of various phenols found are calculated by using tridecane as an internal standard. The emission of phenols from cars running on fuels containing different concentrations of aromatics, and on leaded and lead-free fuels, has also been considered. The results show that the concentration of total phenols is dependent on the type of sample, and is strongly dependent on the concentration of aromatic hydrocarbons and of tetraethyl-lead in the fuel.     

Relationship between the electrochemical and antioxidant activities of alkyl-substituted phenols

Oxidation potentials and rate constants have been determined for reactions between alkyl-substituted phenols with various structures and the styryl peroxy radical. The overall inhibiting activity of the phenols in the thermal autooxidation of lard has been studied. The interrelation between the structure, physicochemical properties, and antioxidant activity of the phenols is discussed.     

Regioselective Nitration of Phenols by NaNO3 in Microemulsion

Highly regiospecific mononitration of phenols and substituted phenols was carried out in TX100-based microemulsion. The use of inexpensive and relatively nontoxic acidic reagent is an advantage of this method. The effect of various parameters such as concentration of NaNO₃, temperature, and agitation speed on reaction system have been investigated. Exclusive ortho-selectivity was observed for all the phenols subjected to this protocol.