The synthesis of tetracyclic coumarins via decarboxylative asymmetric[4+2]cycloadditions enabled by Pd(0)/Cu(I)synergistic catalysis

Tetracyclic coumarins are a class of important compounds with diverse and superior pharmacolog‐ical activities.However,a direct stereoselective method from simple and readily‐made coumarins derivatives remains challenging due to the inertness of coumarins as dienophiles.Herein,we de‐velop a decarboxylative asymmetric[4+2]cycloaddition of 3‐cyanocoumarins with vinyl benzoxa‐zinones,affording the coumarin‐derived condensed rings bearing three continuous stereocenters in high yields with excellent diastereoselectivities(>20/1 d.r.)and enantioselectivities(up to 99%ee).This direct enantioselective reaction was achieved by a Pd(0)/Cu(I)bimetallic catalytic system.The mechanism studies indicated that the synergistic activation effect,in which chiral Cu(I)as an availa‐ble Lewis acid catalyst activates 3‐cyanocoumarin and chiral Pd(0)complex activates benzoxazi‐none by the formation ofπ‐allyl‐palladium intermediate,plays an important role on the stereoselec‐tive control.The current work provides a new activation modes of Cu catalyst in the Pd/Cu bimetal‐lic catalytic system.

Radicals as Chiral Catalysts for Asymmetric Radical Cyclization Reactions

Due to the innate highly reactive properties and short life-time,organic free radicals can often serve as promoters or intermediates to engage in various radical transformations,which are often otherwise difficult to access by ionic pathway-based mechanisms.With the evolvement of radical chemistry,chiral radical catalyzed-transformations have recently emerged as an attractive and robust platform for synthesis of chiral molecules of interest.Herein,we highlight several creative and strategic advances in chiral radical catalyst design,cyclization reaction achievements,and future challenges.

Chiral carbon dots from glucose by room temperature alkaliassisted synthesis for electrocatalytic oxidation of tryptophan enantiomers

Chiral catalysis is one of the most direct and effective approach to obtain pure optical enantiomers.Chiral carbon dots(CDs)as carbon-based chiral catalysts show great potential in chiral catalysis.Herein,we report a facile one step base-catalyzed aldol condensation to fabricate the chiral CDs from glucose at ambient temperature and pressure.The formation of chiral CDs involves the processes of isomerization and aldol condensation.These chiral CDs have been demonstrated that they have selective capacity for electrocatalytic oxidization of tryptophan enantiomers.L type of CDs(LCDs)is more likely to catalyze L-tryptophan(Trp)than D-Trp with the selective factor(I_(L)/I_(D))of 1.60,whereas the D type of CDs(DCDs)tends to catalyze D-Trp(I_(L)/I_(D):0.63).Theoretical calculations combined with various contrast experiments(temperature and pH)demonstrate that the selectively electrocatalytic capacity of chiral CDs toward Trp isomers is due to the different hydrogen-bond interactions between chiral CDs and Trp.

Recent advances in gold-complex and chiral organocatalyst cooperative catalysis for asymmetric alkyne functionalization

Homogeneous gold catalysis has demonstrated the preponderant capability of realizing a broad range of synthetically versatile alkyne functionalization over the last two decades.Though catalytic asymmetric alkyne transformation has focused on the principle of using gold catalysts either associated with chiral phosphine ligand or combined with chiral counterion,a variety of breakthroughs have been reported with the application of gold-complex and chiral organocatalyst cooperative catalysis strategy,which could enable the challenging transformations that cannot be realized by mono-catalysis with excellent stereoselectivity.This review will cover two general protocols in this field,including relay catalysis and synergistic catalysis,with emphasis on the detailed cooperative catalysts models to illustrate the roles of the two catalysts and highlight the potential synthetic opportunities offered by asymmetric cooperative catalysis.

电酶级联催化体系应用于手性环氧化催化

The chiral epoxidation of styrene and its derivatives is an important transformation that has attracted considerable scientific interest in the chemical industry.Herein,we integrate enzymatic catalysis and electrocatalysis to propose a new route for the chiral epoxidation of styrene and its derivatives.Chloroperoxidase(CPO)functionalized with 1-ethyl-3-methylimidazolium bromide(ILEMB)was loaded onto cobalt nitrogen-doped carbon nanotubes(CoN@CNT)to form a biohybrid(CPO-ILEMB/CoN@CNT).H_(2)O_(2)species were generated in situ through a two-electron oxygen reduction reaction(2e–ORR)at CoN@CNT to initiate the following enzymatic epoxidation of styrene by CPO.CoN@CNT had high electroactivity for the ORR to produce H_(2)O_(2)at a more positive potential,prohibiting the conversion of FeⅢ to FeⅡ in the heme of CPO to maintain enzymatic activity.Meanwhile,CoN@CNT could serve as an ideal carrier for the immobilization of CPO-ILEMB.Hence,the coimmobilization of CPO-ILEMB and CoN@CNT could facilitate the diffusion of intermediate H_(2)O_(2),which achieved 17 times higher efficiency than the equivalent amounts of free CPO-ILEMB in bulk solution for styrene epoxidation.Notably,an enhancement(~45%)of chiral selectivity for the epoxidation of styrene was achieved.

Catalytic Enantioselective Simultaneous Control of Axial Chirality and Central Chirality in Allenes

Chiral molecules, which may contain one or more different type（s） of stereocentres, such as central, axial, planar, and helical chiralities, etc., are indispensable in chemistry, pharmaceutical industry, and life science. Despite many advances for the preparation of chiral molecules usually with a single type of chirality have been realized, simultaneous construction of different types of chiralities is still a significant challenge. Here, we wish to report a protocol for preparation of chiral allenes with both central and axial chiralities via a catalytic asymmetric allenylation of different biologically or syn- thetically useful fluorinated or non-fluorinated nucleophiles with readily available racemic allenes by using a single chiral ligand. An echoing between the central chirality and axial chirality for the enantioselectivity was observed. This strategy provides a general and practical approach to functionalized optically active allenes bearing both central and axial chiralities with an excellent enantioselectivity under mild conditions.

Recent catalytic syntheses of trifluoromethylthio-containing organic compounds by transition metals,chiral organocatalysts,and photocatalysts

This review summarizes the recent advances in the catalytic syntheses of CFS-containing organic molecules using various nucleophilic or electrophilic trifluoromethylthiolating reagents.C-halogen and C—H bonds in various molecules have been transformed to C—SCFbonds by transition-metal-catalyzed reactions,such as cross-coupling of aryl halides.Enantioselective reactions controlled by chiral metal complexes or chiral organocatalysts have afforded many trifluoromethylthiolated chiral architectures,such as β-ketoesters and oxindoles.Very recently,visible-light-induced photoredox trifluoromethylthiolations have been developed,providing versatile CFS-containing structures efficiently.

Catalytic Enantioselective Construction of Chiral Benzo-Fused N-Heterocycles through Friedel-Crafts-Type Electrophilic Chlorination

Chiral benzo-fused N-heterocycles are frequently found in natural and synthetic products.However,their synthesis usually suffers from different limitations such as difficulty in accessing appropriate starting materials and unsatisfactory stereoselectivities.In this work,an unprecedented chiral sulfide-catalyzed enantioselective Friedel-Crafts-type electrophilic chlorination is shown to construct various 3,4-functionalized tetrahydroquinolines with excellent enantio-and diastereoselectivities from readily available aniline derivatives.Interestingly,employing N-allyl 1-naphthanilides as substrates,divergent reactions via chlorocarbocyclization and dearomatization occurred to afford two chiral polycyclic benzo-fused N-heterocycles.The system that we developed extends the scope of asymmetric chlorination to general substrateswithout the need of a N-H group,and significantly promotes the synthesis of enantioenriched benzo-fused N-heterocycles.

Diastereoselective alkylation reactions employing a new camphor-based 2-phenylimino-2-oxazolidine chiral auxiliary

A new camphor-based 2-phenylimino-2-oxazolidine chiral auxiliary was prepared and it was shown to be a particularly effective chiral auxiliary for asymmetric alkylations affording high yields and diastereoselectivities. The alkylation products were readily cleaved by simple alkaline hydrolysis to give a-alkylated carboxylic acids in good yield and in almost enatiomerically pure form.

Asymmetric hydroazidation ofα-substituted vinyl ketones catalyzed by chiral primary amine

We report herein the first example of asymmetric hydroazidation of α-substituted vinyl ketones by using chiral primary amines as the catalysts.A simple chiral primary-tertiary diamine catalyst derived from lphenylalanine was found to readily promote this aza-Michael addition reaction with enamine protonation as the key stereogenic step,thus enabling the effective synthesis of α-chiral β-azido ketones with good yields and moderate enantioselectivities.

Asymmetric catalytic anhydride openings via carbon-based nucleophiles

The asymmetric desymmetrization of cyclic anhydrides via the addition of carbon-based nucleophiles has been the focus of considerable levels of interest because it leads to optically active products. Over the past 20 years, a variety of different catalytic asymmetric alkylation reactions have been developed for the desymmetrization of cyclic anhydrides using different metal reagents as nucleophiles and using chiral ligands. The purpose of this review is to provide an overview of significant developments in this field. ~ 2013 Fen-Er Chen. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.