Asymmetric Binary-Acid Catalysis in the Inverse-Electron-Demanding Hetero-Diels-Alder Reaction of 3,4-Dihydro-2H-Pyran

研究了双酸催化剂不对称催化烯醚和β,γ-不饱和α-酮酸酯的反电子Hetero-Diels-Alder（HDA）反应,为手性合成3,4-二氢-2H-吡喃类化合物提供了一种新的催化合成方法.InBr3与手性磷酸钙盐Ca（1c）2组合的手性双路易斯酸催化体系能够有效催化3,4-二氢-2H-吡喃和β,γ-不饱和α-酮酸酯的反电子HDA反应,反应给出优秀的产率（最高达98%）,中等到良好的非对映选择性（最高达89∶11）和良好到优秀的对映选择性（最高可达94%）.并且该双酸催化体系也能成功实现其它烯醚（如：2,3-二氢-2H-呋喃,乙烯基乙醚）的HDA反应,获得优秀的非对映选择性（〉94∶6）和良好的对映选择性.     

铟(I)/手性磷酸催化简单烯烃与β,γ-不饱和α-酮酸酯的不对称[4+2]环加成反应

报道了In（I）Cl/手性磷酸1a双酸体系催化的简单烯烃和β,γ-不饱和α-酮酸酯的不对称[4+2]环加成反应,可高产率、高选择性（最高99：1dr,99%ee）生成相应的exo-[4+2]环加成产物.InCl和磷酸的协同作用是反应成功的关键,单独使用InCl和磷酸都不能催化反应进行.     

Lewis酸对氮杂环卡宾协同催化体系中反应途径的调控

该研究基于氮杂环卡宾（N-heterocyclic carbene,NHC）新颖的协同催化策略,通过Lewis酸共催化剂调控反应具体途径.从α,β-不饱和醛类化合物出发,立足于多反应位点的高烯醇中间体,与氯化镁协作实现高对映选择性的质子转移历程,构建β-手性酯类产物;在相似的反应体系中与氯化钌协作实现高效的空气氧化,构建α,β-不饱和酯类化合物.这两个迥异的反应途径对底物均有较好的官能团容忍性,以高转化率得到目标产物.     

铜/手性磷酸催化烯烃不对称自由基胺芳基化

含β-芳基/α-季碳中心的吡咯烷是一类重要的手性吡咯烷类化合物.目前该类化合物的不对称合成主要是通过钯催化含氮烯烃底物与各类芳基前体的不对称胺芳基化反应来实现的.在这里报道了一种反应机理不同于上述反应的不对称胺芳基化新方法.利用本课题组之前发展的一价铜/手性磷酸组成的金属手性阴离子单电子催化体系成功实现了含氮烯烃底物与芳基重氮盐的不对称自由基的胺芳基化反应,以中等收率和中等至良好的对映选择性得到含β-芳基/α-季碳中心的吡咯烷类化合物.     

铑和手性螺环磷酸协同催化α-芳基重氮酮对醇的O-H键的不对称插入反应

过渡金属催化卡宾对O-H键的不对称插入反应是合成手性醇及其衍生物的直接方法.近年来,人们发展了多种手性催化剂实现了重氮酯衍生的金属卡宾对醇、酚、羧酸甚至水的O-H键的高对映选择性插入反应,但是重氮酮作为卡宾前体的不对称O-H键插入反应鲜有成功的例子.以非手性双铑络合物和手性螺环磷酸组成的协同催化体系,首次实现了α-重氮酮对醇的O-H键的不对称插入反应,获得了较高的收率和高达95%ee的对映选择性.反应为手性α-烷氧基酮这类重要手性化合物提供了高效的合成方法.还通过密度泛函理论计算,对反应机理进行了初步研究,发现水很可能参与了手性磷酸促进的烯醇中间体质子转移过程.     

高对映选择性的有机催化的二氟烯醇硅醚与β,γ-不饱和-α-酮酸酯的不对称Mukaiyama-aldol反应

首次研究了二氟烯醇硅醚1与β,γ-不饱和酮酸酯2的反应.发现不论使用叔胺或叔胺-氢键给体双功能催化剂,均专一地发生Mukaiyama-aldol反应生成相应的叔醇3.利用手性氢化奎宁衍生的双功能脲催化剂11高对映选择性地实现了这一反应,为合成α-二氟烷基取代的手性叔醇提供了一种新方法.不同芳基取代的二氟烯醇硅醚以及γ位不同芳基取代的酮酸酯化合物均反应良好.在所考察的15个例子中,反应产率中等到良好(44%～81%),对映选择性中等到优秀(72%～96%).反应产物可方便转化为二氟烷基取代的手性二醇或三醇化合物.     

有机催化不对称[3+3]环化合成新型光学活性稠合多环3,4-二氢吡喃并[4,3-b]吡喃-5-(2H)-酮（英文）

发展了一种手性双功能方酰胺催化的4-羟基-2(H)-吡喃并[2',3':4,5]吡喃并[2,3-c]吡唑-2,5(7H)-二酮与(E)-2-硝基烯丙基醋酸酯之间的对映选择[3+3]环化反应,为立体选择构筑稠合多环3,4-二氢吡喃并[4,3-b]吡喃-5-(2H)-酮骨架提供了途径.在衍生自(1R,2R)-1,2-二苯基乙-1,2-二胺的手性双功能方酰胺的催化下,以中等至较高产率、高的反式选择性和中等至优秀的对映选择性得到了一系列具有两个连续手性中心的新型稠合多环3,4-二氢吡喃并[4,3-b]吡喃-5-(2H)-酮衍生物.     

1,4-二烯和醛的烯丙基碳氢不对称烷基化反应

利用钯配合物、有机胺和手性布朗斯特酸三元催化剂体系实现了α-取代丙醛参与的1,4-二烯烃的烯丙基碳氢不对称烷基化反应,以良好的产率、优良的区域选择性和立体选择性得到了结构多样的手性α-羰基化合物.此外发现非手性膦配体对钯配合物的催化活性和反应的选择性有十分显著的影响,为后续相关研究提供了新的思路.     

甲基酮的二氟同系化-卤化反应:一锅法合成β-卤代-α,α-二氟代酮

以（溴二氟甲基）三甲基硅烷（TMSCF₂Br）为二氟卡宾源,利用其兼具TMS转移特性及自活化特性,仅在催化量的n-Bu₄NBr的催化启动下,直接完成甲基酮的烯醇化-二氟环丙烷化反应以及与卤正离子的开环卤化反应,并使用卤负离子作为卤源,采用其原位氧化形成卤正离子的方法实现了偕二氟环丙烷硅醚的开环-卤化,合成了β-卤代-α,α-二氟代酮类物质.     

靛红衍生的硝酮与酮亚胺的不对称直接氮杂插烯Mannich反应

不对称直接插烯Mannich反应是一类高效构建手性δ-氨基-α,β-不饱和羰基化合物的方法,但这类反应主要局限于以γ-丁烯酸内酯及类似物和α,α-二氰基烯烃等作为亲核试剂前体,因此发展新的插烯亲核试剂尤为重要.本工作报道了一类从靛红衍生且含N-CH结构的硝酮化合物,由于氧化吲哚骨架的强吸电子效应能在温和碱性条件下生成氮杂二烯醇中间体,高效与靛红衍生的亚胺发生直接氮杂插烯Mannich反应.采用金鸡纳碱衍生的手性双功能叔胺硫脲催化剂,以高收率（70%～97%）、高立体选择性（83%～99% ee,>19∶1 dr）合成富官能团化并含相邻季碳-叔碳手性中心的硝酮化合物,且可进一步与缺电烯烃发生[3+2]偶极环加成反应构建含有氢化异噁唑环的吲哚螺环复杂骨架.这类靛红衍生的硝酮作为氮杂插烯亲核试剂可能在不对称合成中具有更为广阔的应用.     

trans-3,4-Disubstituted pyrrolidines by 1,3-dipolar cycloaddition: enantioselective approaches and their limitations

In the presence of a chiral Lewis acid as co-catalyst, the acid-catalysed 1,3-dipolar cycloaddition reaction yielding trans-3,4-disubstituted pyrrolidines from an azomethine ylide and achiral α,β-unsaturated dipolarophiles proceeded with low enantioselectivity. Therefore a number of α,β-unsaturated dipolarophiles linked to chiral auxiliaries were examined as substrates. Camphorsultam was the best auxiliary and gave good diastereoselectivity (dr=74:26). When combining chiral Lewis acids with a dipolarophile linked to a chiral auxiliary, the enantioselectivity could be slightly increased. As judged by ¹³C NMR, the small effect of the chiral Lewis acids on selectivity was probably due to breakdown of the initially formed complex with the dipolarophile caused by the dipole precursor.     

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.     

Diastereospecific synthesis of 2.6-dideoxy- and 2.4.6-trideoxy-sugars via hetero-diels-alder-reaction

β-Acyloxy-a-phenylthio a,β-unsaturated carbonyl compounds and ethyl-vinylether afforded in a endo-specific hetero-Diels-Alder reaction functionalized 3.4-dihydro-2H-pyrans. These compounds were transfered diastereospecifically into deoxy sugars this way allowing a stereocontrolled generation of up to four chiral centers.     

Trio Catalysis Merging Enamine,Brønsted Acid,and Metal Lewis Acid Catalysis: Asymmetric Three‐Component Aza‐Diels–Alder Reaction of Substituted Cinnamaldehydes,Cyclic Ketones,and Arylamines

A trio catalyst system, composed of arylamine, BINOL‐derived phosphoric acid, and Y(OTf)₃, enables the combination of enamine catalysis with both hard metal Lewis acid catalysis and Brønsted acid catalysis for the first time. Using this catalyst system, a three‐component aza‐Diels–Alder reaction of substituted cinnamaldehyde, cyclic ketone, and arylamine is carried out with high chemo‐ and enantioselectivity, affording a series of optically active 1,4‐dihydropyridine (DHP) derivatives are obtained in 91–99 % ee and 59–84 % yield. DHPs bearing a chiral quaternary carbon center are also obtained with good enantioselectivity and moderate yield (three examples). Preliminary mechanistic investigations have also been conducted.     

Diastereodivergent asymmetric sulfa-Michael additions of α-branched enones using a single chiral organic catalyst

A significant limitation of modern asymmetric catalysis is that, when applied to processes that generate chiral molecules with multiple stereogenic centers in a single step, researchers cannot selectively access the full matrix of all possible stereoisomeric products. Mirror image products can be discretely provided by the enantiomeric pair of a chiral catalyst. But modulating the enforced sense of diastereoselectivity using a single catalyst is a largely unmet challenge. We document here the possibility of switching the catalytic functions of a chiral organic small molecule (a quinuclidine derivative with a pendant primary amine) by applying an external chemical stimulus, in order to induce diastereodivergent pathways. The strategy can fully control the stereochemistry of the asymmetric conjugate addition of alkyl thiols to α-substituted α,β-unsaturated ketones, a class of carbonyls that has never before succumbed to a catalytic approach. The judicious choice of acidic additives and reaction media switches the sense of the catalyst's diastereoselection, thereby affording either the syn or anti product with high enantioselectivity.     

Enantioselective cyanosilylation of ketones catalyzed by double-activation catalysts with N-oxides

Enantioselective addition of trimethylsilyl cyanide to ketones by a catalytic double-activation method is described. By combinatorially using 2.0 mol% of a chiral salen-titanium complex and 1.0 mol% of an achiral tertiary amine N-oxide, aromatic, aliphatic and α,β-unsaturated ketones are converted into corresponding cyanohydrin trimethylsilyl ethers with 50-93% yield and 59-86% ee. The effects of ligand structure, catalyst loading and substrate concentration, solvents, the nature of Lewis base, counter ion and other additives, temperature, and substrate structure on the enantioselectivity are discussed. Three possible paths to achieve the asymmetric version of double-activation catalysis and two independent examples of it are proposed.     

Catalytic asymmetric addition of beta-keto phosphonates to an activated imine--formation of optically active functionalized phosphonate alpha-amino acid derivatives

The direct stereoselective addition of an activated imine to beta-keto phosphonates in the presence of chiral Lewis acid complexes is developed. The evaluation of different activated imines shows that an N-tosyl-alpha-imino ester adds in a diastereo- and enantioselective fashion to beta-keto phosphonates activated by especially chiral copper(II)-bisoxazoline complexes. An evaluation of Lewis acids, chiral ligands and reaction conditions, such as solvent, bases and other additives, shows that high yields, moderate diastereoselectivity and good enantioselectivity are obtained. The scope of the reaction is demonstrated for the reaction of beta-keto phosphonates and finally, the mechanism for the catalytic stereoselective step is presented.     

Iron-catalyzed Michael reactions revisited: a synthetically useful process for the preparation of tri-carbonyl compounds and chiral warfarin

The LBAs (Lewis acid-assisted Brønsted acid catalysis) is proposed as possible mechanistic process in the simple FeCl₃-catalyzed Michael reactions of chalcones with active methylene compounds in organic solvents. And iron salts were found to be effective promoters in the asymmetric Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketone, which resulted in excellent yield and high level of enantioselectivity (up to 91% ee) in the presence of low catalytic amount of iron and simple chiral primary amine.     

A practical synthetic route to functionalized THBCs and oxygenated analogues via intramolecular Friedel-Crafts reactions

A practical catalytic approach to the synthesis of 4-substituted 1,2,3,4-tetrahydro-beta-carbolines (THBCs, 1) and 1,2,3,9-tetrahydropyrano[3,4-b]indoles (2) via InBr3-catalyzed intramolecular Friedel-Crafts (F-C) cyclization is described. The use of cross-metathesis reaction represents a direct route to the cyclization precursors and the use of InBr3 (5 mol%) allowed polycyclic indole compounds to be isolated in high yields under mild reaction conditions (rt, DCM, minutes). Finally, efforts toward the development of a stereocontrolled version of the present cyclization are presented, highlighting [salenAlCl] and bimetallic [(salenAlCl)2-InBr3] system as promising chiral Lewis acids (ee up to 60%).     

Chiral Brønsted acid catalyzed enantioselective Mannich-type reaction

Mannich-type reaction of ketene silyl acetals with aldimines proceeded catalytically by means of a phosphoric acid diester, derived from (R)-BINOL, as a chiral Br?nsted acid to afford beta-amino esters with good diastereoselectivity in favor of the syn isomer and high enantioselectivity (up to 96% ee). The highest enantioselectivity was achieved by the phosphoric acid diester bearing 4-nitrophenyl groups on the 3,3'-positions of BINOL. The N-2-hydroxyphenyl group of aldimine was found to be essential for the present Mannich-type reaction. In combination with these experimental investigations, two possible monocoordination and dicoordination pathways were explored using density functional theory calculations (BHandHLYP/6-31G*). The present reaction proceeds via a dicoordination pathway through the zwitterionic and nine-membered cyclic transition state (TS) consisting of the aldimine and the phosphoric acid. The re-facial selectivity was also well-rationalized theoretically. The nine-membered cyclic structure and aromatic stacking interaction between the 4-nitrophenyl group and N-aryl group would fix the geometry of aldimine on the transition state, and the si-facial attacking TS is less favored by the steric hindrance of the 3,3'-aryl substituents.