手性磷酸在不对称反应中的应用

手性磷酸催化剂因其在不对称催化反应中表现出的高效、高对映选择性而受到人们越来越多的关注.含1,1'-联二萘酚(BINOL)骨架的手性磷酸类催化剂已被广泛用于亚胺的不对称氢转移、Friedel-Crafts反应和Mannich反应等许多重要的有机合成反应.手性磷酸具有同时提供质子和接受质子的双功能作用,因此可以同时活化两个反应底物.含BINOL骨架的手性磷酸可以通过改变BINOL骨架3,3'-位上的取代基调控空间位阻和手性磷酸的酸性,因此可以调节反应的对映选择性.为了合理地设计新的手性磷酸催化剂,扩大其应用范围,最近人们对手性磷酸不对称催化反应机理进行了初步的理论计算研究并取得了显著进展.综述了手性磷酸在不对称反应中的部分研究工作,尤其是理论研究领域的最新成果.     

Acid-base catalysis of chiral Pd complexes: development of novel catalytic asymmetric reactions and their application to synthesis of drug candidates

Using the unique character of the chiral Pd complexes 1 and 2, highly efficient catalytic asymmetric reactions have been developed. In contrast to conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine and methylene compounds were activated to form chiral palladium enolates, which underwent enantioselective carbon-carbon bond-forming reactions such as Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid, formed concomitantly during the formation of the enolates to activate electrophiles, thereby promoting the C-C bond-forming reaction. This palladium enolate chemistry was also applicable to electrophilic enantioselective fluorination reactions, and various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, tert-butoxycarbonyl lactone/lactams, cyanoesters, and oxindole derivatives could be fluorinated in a highly enantioselective manner (up to 99% ee). Using this method, the catalytic enantioselective synthesis of BMS-204352, a promising anti-stroke agent, was achieved. In addition, the direct enantioselective conjugate addition of aromatic and aliphatic amines to alpha,beta-unsaturated carbonyl compound was successfully demonstrated. In this reaction, combined use of the Pd complex 2 having basic character and the amine salt was the key to success, allowing controlled generation of the nucleophilic free amine. This aza-Michael reaction was successfully applied to asymmetric synthesis of the CETP inhibitor torcetrapib.     

Electronic helix theory-guided rational design of kinetic resolutions by means of the Sharpless asymmetric dihydroxylation reactions

Kinetic resolution represents a key chemical reaction strategy for asymmetric synthesis of optically enriched compounds, and it originates from a simple phenomenon that a pair of mirror images (enantiomers) of a racemate can react with different rates under a chiral environment. While highly efficient catalytic kinetic resolutions by means of the classical Sharpless asymmetric epoxidation (AE) reactions are well established in modern organic synthesis, such systems based on the arguably more versatile Sharpless asymmetric dihydroxylation (AD) processes, although long pursued and widely attempted, remain largely underexplored. With insights gained from a new electronic helix theory we recently developed for molecular chirality and chiral interactions, we were able to advance a proposal suggesting why this problem is challenging and how it might be solved. Guided by a new design concept aimed at identifying complimentary catalyst–substrate electronic interactions, we reported herein that not only can such elusive systems be generally feasible, but efficiencies well reach the highest levels known to date with chemical or enzymatic kinetic resolutions of any type.     

Combinatorial chemistry approach to chiral catalyst engineering and screening: rational design and serendipity

An efficient asymmetric catalyst relies on the successful combination of a large number of interrelated variables, including rational design, intuition, persistence, and good fortune-not all of which are necessarily well-understood; this renders such practice largely empirical. As a result, the possibility of using combinatorial chemistry methods in asymmetric catalysis research has been widely recognized to be highly desirable. In this account, we attempt to show the principle and application of combinatorial approach in the discovery of chiral catalysts for enantioselective reactions. The concept focuses on the strategy for the creation of a modular chiral catalyst library by two-component ligand modification of metal ions on the basis of molecular recognition and assembly. The self-assembled chiral catalyst with two different ligands indeed exhibited synergistic effects in terms of both enantioselectivity and activity in comparison with its corresponding homocombinations in many reactions. The examples described in this paper demonstrated the powerfulness of combinatorial approach for the discovery of novel chiral catalyst systems, particularly for the development of highly efficient, enantioselective, and practical catalysts for enantioselective reactions. We hope this concept will stimulate further work on the discovery of more highly efficient and enantioselective catalysts, as well as unexpected classes of catalysts or catalytic enantioselective reactions in the future with the help of a combinatorial chemistry approach.     

Enantioselective total synthesis of (+)-tricycloclavulone

The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner. It includes a catalytic enantioselective [2+2]-cycloaddition reaction using novel chiral copper catalyst, extremely effecting an intramolecular ester transfer reaction, and asymmetric reduction of the carbonyl group on the alpha-chain using Noyori's chiral ruthenium catalyst.     

Development of Chiral Organosuperbase Catalysts Consisting of Two Different Organobase Functionalities

In the field of chiral Brønsted base catalysis, a new generation of chiral catalysts has been highly anticipated to overcome the intrinsic limitation of pronucleophiles that are applicable to the enantioselective reactions. Herein, we reveal conceptually new chiral Brønsted base catalysts consisting of two different organobase functionalities, one of which functions as an organosuperbase and the other as the substrate recognition site. Their prominent activity, which stems from the distinctive cooperative function by the two organobases in a single catalyst molecule, was demonstrated in the unprecedented enantioselective direct Mannich‐type reaction of α‐phenylthioacetate as a less acidic pronucleophile. The present achievement would provide a new guiding principle for the design and development of chiral Brønsted base catalysts and significantly broaden the utility of Brønsted base catalysis in asymmetric organic synthesis.     

Highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate: a cooperative catalysis approach

The cooperative catalyst activity between a chiral transition-metal catalyst and an achiral organocatalyst has been identified as one of the critical asymmetric reaction optimization components in the highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate.     

Bifunctional transition metal-based molecular catalysts for asymmetric syntheses

The discovery and development of conceptually new chiral bifunctional transition metal-based catalysts for asymmetric reactions is described. The chiral bifunctional Ru catalyst was originally developed for asymmetric transfer hydrogenation of ketones and imines and is now successfully applicable to enantioselective C-C bond formation reaction with a wide scope and high practicability. The deprotonation of 1,3-dicarbonyl compounds with the chiral amido Ru complexes leading to the amine Ru complexes bearing C- or O-bonded enolates, followed by further reactions with electrophlies gives C-C bond formation products. The present bifunctional Ru catalyst offers a great opportunity to open up new fundamentals for stereoselective molecular transformation including enantioselective C-H and C-C as well as C-O, C-N bond formation.     

Asymmetric synthesis of pharmaceutically relevant 1-aryl-2-heteroaryl- and 1,2-diheteroarylcyclopropane-1-carboxylates

This study describes general methods for the enantioselective syntheses of pharmaceutically relevant 1-aryl-2-heteroaryl- and 1,2-diheteroarylcyclopropane-1-carboxylates through dirhodium tetracarboxylate-catalysed asymmetric cyclopropanation of vinyl heterocycles with aryl- or heteroaryldiazoacetates. The reactions are highly diastereoselective and high asymmetric induction could be achieved using either (R)-pantolactone as a chiral auxiliary or chiral dirhodium tetracarboxylate catalysts. For meta- or para-substituted aryl- or heteroaryldiazoacetates the optimum catalyst was Rh₂(R-p-Ph-TPCP)₄. In the case of ortho-substituted aryl- or heteroaryldiazoacetates, the optimum catalyst was Rh₂(R-TPPTTL)₄. For a highly enantioselective reaction with the ortho-substituted substrates, 2-chloropyridine was required as an additive in the presence of either 4 Å molecular sieves or 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Under the optimized conditions, the cyclopropanation could be conducted in the presence of a variety of heterocycles, such as pyridines, pyrazines, quinolines, indoles, oxadiazoles, thiophenes and pyrazoles.

The dirhodium tetracarboxylate-catalysed asymmetric cyclopropanation has been applied to the enantioselective syntheses of pharmaceutically relevant 1-aryl-2-heteroaryl- and 1,2-diheteroarylcyclopropane-1-carboxylates.     

Enantioselective Hydroamidation of Enals by Trapping of a Transient Acyl Species

An enantioselective synthesis of β‐chiral amides through asymmetric and redox‐neutral hydroamidation of enals is reported. In this reaction, a chiral N‐heterocyclic carbene (NHC) catalyst reacts with enals to generate the homoenolate intermediate. Upon highly enantioselective β‐protonation through proton‐shuttle catalysis, the resulting azolium intermediate reacts with imidazole to yield the key β‐chiral acyl species. This transient intermediate provides access to diversified β‐chiral carbonyl derivatives, such as amides, hydrazides, acids, esters, and thioesters. In particular, β‐chiral amides can be prepared in excellent yield and ee (40 chiral amides, up to 95 % yield and 99 % ee). This modular strategy overcomes the challenge of disruption of the highly selective proton‐shuttling process by basic amines.     

Highly Enantioselective Hydrogenation of Cyclic Enol Acetates Catalyzed by a Rh–PennPhos Complex

The electron‐rich and conformationally rigid (R,S,R,S)‐Me‐PennPhos ligand (shown schematically) appears to chelate rhodium and form well‐defined chiral pockets. This allows, for example, efficient differentiation between the two enantiotopic approaches available to a substrate in a hydrogenation reaction. The Rh–Me‐PennPhos complex is the first catalyst for the highly enantioselective asymmetric hydrogenation of cyclic enol acetates. For example, 3,4‐dihydronaphth‐1‐yl acetate can be hydrogenated with up to 99% ee.     

手性磷酸催化的有机催化不对称反应

手性磷酸是近年来发展起来的一类新型高效、高对映选择性的Brønsted酸类有机催化剂, 已成功应用于催化不对称Mannich反应、还原胺化反应、Pictet-Spengler反应、aza-Diels-Alder反应和aza-Ene反应等许多重要的有机合成反应. 手性磷酸催化剂分子内同时含有Lewis碱性位点和Brønsted酸性位点, 可同时活化亲电与亲核底物. 作为一种新型双功能有机催化剂, 手性磷酸具有较高的催化活性和对映选择性, 催化剂最低用量可达0.05 mol%. 对各类手性磷酸催化剂在有机催化不对称合成反应中的应用研究进展, 以及不对称诱导反应的机理、手性磷酸的分子结构及反应条件对其催化活性和不对称诱导活性的影响进行了评述.     

Catalytic enantioselective peroxidation of alpha,beta-unsaturated ketones

Despite the potential of chiral peroxides as biologically interesting or even clinically important compounds, no catalytic enantioselective peroxidation has been reported. With a chiral catalyst not only to induce enantioselectivity but also to convert a well established epoxidation pathway into a peroxidation pathway, the first efficient catalytic peroxidation has been successfully developed. Employing readily available alpha,beta-unsaturated ketones and hydroperoxides and an easily accessible cinchona alkaloid catalyst, this novel reaction will open new possibilities in the asymmetric synthesis of chiral peroxides. Under different conditions a highly enantioselective epoxidation with the same starting materials, reagents, and catalyst has was also established.     

Low Coordination State RhI-Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta-Substituted Cyclopropanes

A simple, broad-scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri-substituted allylic diazoacetates was successfully developed. The low coordination state Rh^I-complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta-substituted, fused-ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol %. The stereoinduction mode of this Rh^I-carbene-directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π-π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.     

A Versatile Enantioselective Catalytic Cyclopropanation-Rearrangement Approach to the Divergent Construction of Chiral Spiroaminals and Fused Bicyclic Acetals

A highly enantioselective synthesis of various chiral heterobicyclic molecules including spiroaminals and fused bicyclic acetals has been developed via a chiral copper catalyzed cyclopropanation-rearrangement (CP-RA) approach under mild reaction conditions. Remarkably, the asymmetric CP-RA for exocyclic vinyl substrates without a pro-stereogenic carbon at the β-position has been realized for the first time and a broad substrate scope with excellent results (33 examples; 34–99 % yields; >95/5 dr and 91–99 % ee) has been achieved. An application of a successive enantioselective CP-RA approach was also described, providing a concise access to complex chiral heteropolycycles.     

Enantioselective Synthesis of a Chiral Coordination Polymer with Circularly Polarized Visible Laser

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL‐responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL‐induced enantioselective synthesis. By irradiation with either left‐handed or right‐handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left‐handed CPL resulted in crystals with a left‐handed helical structure, and right‐handed CPL led to crystals with a right‐handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers.     

Asymmetric Mannich reactions with in situ generation of carbamate-protected imines by an organic catalyst

The instability of carbamate-protected alkyl imines has greatly hampered the development of catalytic asymmetric Mannich reactions suitable for the synthesis of optically active carbamate-protected chiral alkyl amines. A highly enantioselective Mannich reaction with in situ generation of carbamate-protected imines from stable alpha-amido sulfones catalyzed by an organic catalyst was developed. This reaction provides a concise and highly enantioselective route converting aromatic and aliphatic aldehydes into optically active aryl and alkyl beta-amino acids. [reaction: see text].     

Catalytic Asymmetric Iodoesterification of Simple Alkenes

Catalytic asymmetric iodoesterification of simple alkenes was achieved using a dinuclear zinc‐3,3′‐(R,S,S)‐bis(aminoimino)binaphthoxide ( di‐Zn ) complex. For iodoesterification using p‐methoxybenzoic acid, the N‐iodonaphthalenimide (NIN)‐I₂ system was effective for producing iodoesters in a highly enantioselective manner. The synthetic utility of chiral iodo‐p‐methoxybenzoates was also demonstrated. The quartet of metal ionic bond, hydrogen bond, halogen bond, and π‐π stacking is harmonized on the single reaction sphere of di‐Zn catalyst for enabling the highly enantioselective catalytic asymmetric iodoesterification of simple alkenes for the first time.     

Chiral nickel(II) complex catalyzed asymmetric (3 + 2) cycloaddition of α‐diazo pyrazoleamides with 2‐siloxy‐1‐alkenes

A highly efficient asymmetric (3 + 2) cycloaddition of α-diazo pyrazoleamides with silyl enol ethers was realized by employing a chiral N,N'-dioxide-Ni(II) complex catalyst. The process includes the formation of chiral nickel carbenoid intermediate and the following enantioselective cycloaddition reaction. The desired dihydrofuran O,O-acetal derivatives were obtained in good yields (up to 90%) with high enantioselectivity (up to 99% ee) under mild reaction conditions within short reaction time. On the basis of the determination of the catalyst structure, a possible transition state mode was proposed.     

Organocatalytic enantioselective Diels-Alder reaction of dienes with alpha-(N,N-Diacylamino)acroleins

Catalytic and highly enantioselective Diels-Alder reaction of cyclic and acyclic dienes with alpha-phthalimidoacroleins provides cyclic alpha-quaternary alpha-amino acid precursors. The conformationally flexible chiral ammonium salt of H-L-Phe-L-Leu-N(CH(2)CH(2)) 2-reduced triamine with pentafluorobenzensulfonic acid is very effective as an asymmetric catalyst for the Diels-Alder reaction.