Lewis碱协助的Lewis酸催化醇脱水合成烯烃及二氢吡喃开环合成2-肉桂基取代1,3-二羰基化合物（英文）

醇脱水是合成烯烃的重要方法之一.全球每年约有15%的苯乙烯是通过1-苯乙醇在酸性条件下脱水反应生产.虽然人们对该反应进行了较为深入的研究,但是当使用活性较高的1-苯乙醇衍生物为底物时,由于得到的取代苯乙烯产物具有较高的反应性,在脱水过程中会发生聚合而导致反应选择性降低,因此有必要探索适宜在高活性1-苯基乙醇脱水反应中应用的催化剂体系.本文借助酸碱协同催化方法考察了1-(4-甲氧基苯基)乙醇制备4-甲氧基苯乙烯的反应.发现三苯基磷与AlC l3构建的Lewis碱/Lewis酸协同催化体系在硝基甲烷中可以接近定量的收率得到4-甲氧基苯乙烯.Lewis碱/Lewis酸协同催化体系有效避免了4-甲氧基苯乙烯的二聚现象.底物拓展研究显示该方法具有很好的底物普适性,对多种取代苯乙烯的收率均超过80%.机理研究表明,1-(4-甲氧基苯基)乙醇在酸作用下先生成碳正离子,三苯基磷作为偶极性的电子给体不但能在一定程度上稳定该苄基碳正离子,而且抑制了其与4-甲氧基苯乙烯之间的亲电反应,进而最大化了脱质子生成4-甲氧基苯乙烯的选择性.将Lewis碱协助的Lewis酸催化提高反应选择性策略用于2-苯基-3,4-二氢吡喃衍生物合成2-肉桂基-1,3-二羰基化合物的开环反应.该类取代二氢吡喃在酸催化剂作用下也可生成苄基碳正离子,但是该中间体易受分子间和分子内亲电反应影响,反应选择性不高.而当使用单质碘/三苯基磷协同催化体系时,2-苯基-3,4-二氢吡喃衍生物能高选择性地实现开环反应,得到反式2-肉桂基-1,3-二羰基化合物.该类1,3-二羰基化合物具有丰富的反应性,是一类重要的合成子.     

5,6-二氢-5-氧杂-1,3-二氮杂菲衍生物的合成

以2,3-二氢-3-氧代-1,3-苯并(c)-α-吡喃(1)为起始原料, 在氢化钠作用下, 通过与羰基α-氢的Claisen缩合反应, 得到3-乙酰基-2,3-二氢-3-氧代-1,3-苯并(c)-α-吡喃(2), 所得β-二酮与脲、硫脲和脒衍生物分别进行缩合关环, 生成5,6-二氢-5-氧杂-1,3-二氮杂菲衍生物3和4. 在相同的条件下, 吡喃酮1与草酸二乙酯进行缩合反应, 给出3-乙氧乙二酰 基-2,3-二氢-3-氧代-1,3-苯并(c)-α-吡喃(5), 选择3-氨基吡唑、2-氨基咪唑、3-氨基三唑、2-氨基苯并咪唑和3,5-二氨基吡唑-4-偶氮苯与5缩合, 分别环合成5,6-二氢-5-氧杂-1,3-二氮杂菲并和五元含氮杂环衍生物6～10. 所合成的新化合物均经核磁共振光谱、红外光谱及元素分析证明其结构.     

手性方酰胺催化环状1,3-二羰基化合物对β,γ-不饱和-α-酮酯的不对称Michael加成反应（英文）

发展了新型手性双功能叔胺-方酰胺催化的环状1,3-二羰基化合物和β,γ-不饱和-α-酮酯之间的不对称Michael加成反应,反应条件温和,底物适用范围广泛,相应产物的产率和对映选择性分别高达97%和97%ee,为合成和医药上极为重要的手性色烯衍生物的立体选择性合成提供了一种实用的方法.     

哌啶乙酸盐催化合成2,3-二取代-苯并二氢吡喃-4-酮和2,2-二取代-苯并呋喃-3-酮类衍生物

发展了一种以哌啶乙酸盐为催化剂,催化邻羟基苯基β-二酮和不同系列醛进行Knoevenagel与O-Micheal串联反应的新方法,以较好的底物适应性及中等以上的产率,合成了16个2,3-二取代苯并二氢吡喃-4-酮和9个2,2-二取代苯并呋喃-3-酮类衍生物,并且该串联反应合成途径简捷,反应条件温和,催化剂廉价易得.     

铜催化炔丙醇酯与β-羰基膦酸酯的不对称[3+2]环加成反应合成手性膦酰化2,3-二氢呋喃

手性2,3-二氢呋喃衍生物是一类重要的杂环化合物,广泛存在于天然产物和生物活性分子中.它们也经常被用于手性四氢呋喃化合物的不对称合成.因此,人们发展了很多合成手性2,3-二氢呋喃化合物的方法,如有机小分子催化的多米诺迈克尔-烷基化反应、“中断的”Feist-Bénary反应或改进的 Feist-Bénary反应.此外,过渡金属催化的手性2,3-二氢呋喃的不对称合成在近些年引起了人们的极大关注. Ozawa等通过 Pd-催化2,3-二氢呋喃的动力拆分方法获得了手性2-芳基-2,3-二氢呋喃. Evans发展了一种 Sc-催化联烯硅和乙醛酸乙酯的[3+2]环加成反应合成手性2,3-二氢呋喃的方法.最近, Fu和 Tang等发展了 Cu催化烯酮和重氮化合物的[4+1]环加成反应合成手性2,3-二氢呋喃的方法.在 Nishibayashi和 van Maarseveen的开创性工作之后, Cu催化的不对称炔丙基转化反应取得了很大的进展.最近,我们发展了一类新的三齿手性 P,N,N-配体,在 Cu催化不对称炔丙基取代、脱羧炔丙基取代、[3+2]、[3+3]和[4+2]环加成反应中表现出优秀的对映和非对映选择性.其中,我们发现采用 Cu催化炔丙醇酯和β-酮酯的[3+2]环加成反应,能高对映选择性地获得手性2,3-二氢呋喃.我们设想,采用β-羰基膦酸酯代替β-酮酯,通过这种 Cu催化[3+2]环加成反应,将可以合成一类具有重要生物活性的手性膦酰化2,3-二氢呋喃化合物.基于这种设想,本文使用手性 P,N,N-配体,通过 Cu催化炔丙醇酯与β-羰基膦酸酯的不对称[3+2]环加成反应,以很好的收率和最高92% ee的对映选择性获得了一系列光学活性的膦酰化2,3-二氢呋喃化合物.我们以炔丙醇酯1a与β-羰基膦酸酯2a为标准底物,优化了反应条件,考察了配体、Cu盐、碱和反应温度等对反应收率和对映选择性的影响.我们确定了最佳的反应条件：以4b为配体,以 Cu(OTf)2为铜盐,以t-BuOK为碱,以 MeOH为溶剂,–20oC反应24 h.在此条件下,我们对β-羰基磷酸酯2的适用范围进行了考察.结果表明,各种苯基取代的β-羰膦磷酸酯均能得到很好的收率和对映选择性.苯环上取代基的空间效应对反应的对映选择性影响不大,但对反应收率影响较大,与相应3-取代或4-取代底物相比较,2-取代的底物获得的收率较低.苯环对位取代基的电子效应对反应的影响不大,给电子基或吸电子基的底物,均得到了较好的收率和对映选择性.杂环取代的底物同样适用于该反应,以90%的收率和89% ee的对映选择性获得了相应的[3+2]环加成产物.对于烷基底物,虽然反应的产率略低,但是得到了高达92% ee的产物.此外,我们对炔丙醇酯底物的适用范围也进行了考察.结果表明,该体系对于各种取代的炔丙醇酯底物均可以获得较高的收率和良好的对映选择性.总之,本文发展了一种铜催化炔丙醇酯与β-羰基膦酸酯的不对称[3+2]环加成反应的方法,成功合成了手性膦酰化2,3-二氢呋喃化合物.通过使用一个结构刚性的酮亚胺三齿 P,N,N-配体,以很好的收率和最高92% ee的对映选择性获得了一系列光学活性的膦酰化2,3-二氢呋喃化合物.     

2-氨基-3-氰基-4-芳基-6-甲氧基-1,4,9,10-四氢萘并[2,1-b]吡喃衍生物的一步合成

以芳醛、丙二腈和7-甲氧基-1,2,3,4-四氢萘-2-酮为原料,在六氢吡啶催化下以乙醇为溶剂,在室温合成了一系列新的2-氨基-3-氰基-4-芳基-6-甲氧基-1,4,9,10-四氢萘并[2,1-b]吡喃衍生物,反应条件温和,产率较高,并通过IR,1H NMR和元素分析表征产物的结构,还通过单晶X射线衍射分析确证产物的构象.     

磺酰胺为烷基化试剂高选择性合成多取代烯烃和2,3-二氢茚衍生物的方法

在质子酸H_2SO_4催化下,含β氢醇与磺酰胺反应可高选择性地得到三取代烯烃和2,3-二氢茚衍生物.含β氢醇酸性条件下脱水后与磺酰胺发生偶联,可以选择性地合成热力学稳定产物Z-多取代烯烃;两者发生[3+2]环加成反应,则可高选择性地得到2,3-二氢茚衍生物.     

合成文拉法星的2-氮杂-1,3-丁二烯杂Diels-Alder反应与其 单分子环合竞争反应的研究

研究了不同的Lewis酸催化剂、温度、微波等条件下, 4-(4-甲氧苯基)-1-苯基-3-三甲基硅氧基-2-氮杂-1,3-丁二烯(2-ABDE)和亲二烯体环己酮发生杂Diels-Alder反应生成[4＋2]的六元环合产物噁嗪酮衍生物, 伴随的2-ABDE的 [2＋2]单分子环合, 生成单环β-内酰胺衍生物. 结果表明: 在低温条件下如(－78 ℃)[4＋2]反应占主导; 而在高温条件下(如135 ℃)仅进行[2＋2]反应. 微波加热方式可显著提高[2＋2]反应的速率和产率. 不同的Lewis酸催化剂对[2＋2]反应和[4＋2]反应的催化效率不同. Lewis酸的酸性强弱、软硬对2-ABDE的[2＋2]反应的催化能力起决定性作用.     

1,1-二(4-甲基苯基)乙烯的合成及其对碳正离子稳定性的影响

本文通过对甲基溴化镁格氏试剂与对甲基苯乙酮反应,制备出中间产物1,1-二(4-甲基苯基)乙醇;中间产物进一步脱水制备出目标产物1,1-二(4-甲基苯基)乙烯。考察了脱水温度对产率的影响;研究了1,1-二(4-甲基苯基)乙烯封端后碳正离子的稳定性。结果表明,脱水温度在180℃以下,产率随着温度的升高而增加;当脱水温度高于180℃时,产率下降;核磁、红外谱图证实了目标产物。聚异丁烯活性中心通过1,1-二(4-甲基苯基)乙烯封端后,碳正离子活性中心存活时间显著延长;24h后仍能继续引发异丁烯聚合。     

新型苯并二氢呋喃合二酮酸类化合物的合成及其与整合酶分子对接研究

以阿魏酸甲酯为原料,通过氧化偶联构建2-芳基苯并二氢呋喃骨架,再经傅克酰基化和酯缩合反应依次制得(E)-3-［2-(4-羟基-3-甲氧基-5-乙酰基)苯基-3-甲氧羰基-7-甲氧基-2,3-二氢苯［b］并呋喃-5-基］丙烯酸甲酯（3）和(E)-3-［2-(4-羟基-3-甲氧基-5-甲氧羰基乙酰基)苯基-3-甲氧羰基-7-甲氧基-2,3二氢苯并［b］呋喃-5-基］丙烯酸甲酯（4）; 4经水解反应合成3-【2-羟基-3-甲氧基-5-｛5-［2-（甲氧基羰基）乙烯基］-7-甲氧基-3-甲氧羰基-2,3-二氢苯并［b］呋喃-2-｝基】苯基-3-氧丙酸（5）,化合物3~5未见文献报道,其结构经¹H NMR, ¹³C NMR和MS(ESI)表征。采用分子对接软件Autodock vina对化合物2~5与HIV-1整合酶核心部位高度同源的PFV IN（PDB: 3L2V）进行对接,计算结果显示该类化合物能与整合酶形成稳定的复合物,具有1,3-二酮基团的化合物3, 4和5能与整合酶中金属离子产生螯合作用,其中化合物5的结合作用最强。     

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5‐Hydroxymethylfurfural over Mesoporous Nb and Nb‐W Oxides

A series of mesoporous Nb and Nb‐W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5‐hydroxymethylfurfural (HMF ). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb‐W oxides varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Brønsted to Lewis acid sites. All Nb‐W oxides show a relatively high selectivity of HMF , whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2‐butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2‐butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.     

Investigation of Lewis Acid versus Lewis Base Catalysis in Asymmetric Cyanohydrin Synthesis

The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}₂] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X=EtOSO₃ or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}₂O] and triphenylphosphine oxide, a non‐linear Hammett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron‐deficient. These results suggested that the aluminium complex/triphenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ketones and this was found to be the case.     

Direct Mannich‐Type Reactions Promoted by Frustrated Lewis Acid/Brønsted Base Catalysts

Direct Mannich‐type reactions that afford both α‐ and β‐amino esters by the reaction of a broad range of carbonyl compounds and aldimines are disclosed. The transformation is promoted by a sterically frustrated Lewis acid/Brønsted base pair, which is proposed to operate cooperatively: Within the catalyst complex, an enolate is generated that then reacts with a hydrogen‐bond‐activated imine. Noncovalent interactions between reactants and the catalyst provide selectivity and new opportunities for future catalyst design.     

Terbium–organic framework as heterogeneous Lewis acid catalyst for β‐aminoalcohol synthesis: Efficient,reusable and green catalytic method

A terbium–organic framework (Tb‐MOF) was prepared using a previously reported procedure. Tb‐MOF was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, powder X‐ray diffraction and surface area analysis. Tb‐MOF was employed as a heterogeneous Lewis acid catalyst for the synthesis of β‐aminoalcohols. Also, the effect of ultrasonic irradiation was examined in the catalytic aminolysis of styrene oxide. The reaction conditions were optimized by variation of reaction time, catalyst concentration and solvent. A variety of β‐aminoalcohols were synthesized and characterized. The Tb‐MOF catalyst showed excellent selectivity and high yield for these transformations.     

Lewis Acid Catalyzed Selective Reactions of Donor–Acceptor Cyclopropanes with 2‐Naphthols

Lewis acid‐catalyzed reactions of 2‐substituted cyclopropane 1,1‐dicarboxylates with 2‐naphthols is reported. The reaction exhibits tunable selectivity depending on the nature of Lewis acid employed and proceed as a dearomatization/rearomatization sequence. With Bi(OTf)₃ as the Lewis acid, a highly selective dehydrative [3+2] cyclopentannulation takes place leading to the formation of naphthalene‐fused cyclopentanes. Interestingly, engaging Sc(OTf)₃ as the Lewis acid, a Friedel–Crafts‐type addition of 2‐naphthols to cyclopropanes takes place, thus affording functionalized 2‐naphthols. Both reactions furnished the target products in high regioselectivity and moderate to high yields.     

Calcium‐Based Lewis Acid Catalysts

Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf₂)₂, Ca(OTf)₂, CaF₂ and Ca[OCH(CF₃)₂]₂ have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare‐earth metals or strong Brønsted acids.     

Enantioselective Direct Mannich‐Type Reactions Catalyzed by Frustrated Lewis Acid/Brønsted Base Complexes

An enantioselective direct Mannich‐type reaction catalyzed by a sterically frustrated Lewis acid/Brønsted base complex is disclosed. Cooperative functioning of the chiral Lewis acid and achiral Brønsted base components gives rise to in situ enolate generation from monocarbonyl compounds. Subsequent reaction with hydrogen‐bond‐activated aldimines delivers β‐aminocarbonyl compounds with high enantiomeric purity.     

Lewis and Brønsted Acid Cocatalyzed Reductive Deoxyallenylation of Propargylic Alcohols with 2‐Nitrobenzenesulfonylhydrazide

Reductive deoxyallenylation of sterically hindered tertiary propargylic alcohols was realized on reaction with 2‐nitrobenzenesulfonylhydrazide (NBSH) by the combined use of Lewis and Brønsted acid catalysts. This method features a broad substrate scope, mild reaction conditions, and good functional‐group tolerance, and affords various mono‐, di‐, and trisubstituted allenes in good‐to‐excellent yields. The synthetic utility of this method was demonstrated by the synthesis of 2H‐chromenes and 1,2‐dihydroquinolines.     

Lewis acid-promoted intermolecular carbonyl-ene reaction of enantiopure 4-oxoazetidine-2-carbaldehydes. Rapid entry to novel fused polycyclic beta-lactams

Lewis acid-promoted carbonyl-ene reaction of enantiomerically pure 4-oxoazetidine-2-carbaldehydes with various activated alkenes gives 4-[(1'-hydroxy)homoallyl]-beta-lactams with a very high level of syn diastereofacial selectivity. The above homoallylic alcohols are used for the diastereoselective preparation of fused bicyclic, tricyclic, and tetracyclic beta-lactams of nonconventional structure using tandem one-pot radical addition/cyclization or elimination-intramolecular Diels-Alder sequences. In addition, a novel domino process was discovered, the C4-N1 beta-lactam bond breakage/intramolecular Diels-Alder reaction.     

Biased Lewis Pairs: A General Catalytic Approach to Ether‐Ester Block Copolymers with Unlimited Ordering of Sequences

Polymerizing epoxides after cyclic esters remains a major challenge, though their block copolymers have been extensively studied and used for decades. Reported here is a simple catalytic approach based on a metal‐free Lewis pair that addresses the challenge. When the Lewis acid is used in excess of a base, selective (transesterification‐free) polymerization of epoxides occurs in the presence of esters, while selectivity toward cyclic esters is achieved by an oppositely biased catalyst. Hence, one‐pot block copolymerization can be performed in both ester‐first and ether‐first orders with selectivity being switchable at any stage, yielding ether‐ester‐type block copolymers with unlimited ordering of sequences as well as widely variable compositions and architectures. The selectivity can also be switched back and forth several times to generate a multiblock copolymer. Experimental and calculational results indicate that the selectivity originates mainly from the state of catalyst‐activated hydroxy species.