氧化亚锡催化酯化反应

锡的氧化物的催化作用较少报道,较成功的有使用氧化锡与氧化铬组成的二元催化剂催化氧化,氧化亚锡催化硝基苯还原及交酯的聚合。但用于催化酯化,只有用特定方     

Acid‐Acid‐Catalyzed Tandem Reactions Driven by an Additive‐Like Component

Acid‐catalyzed tandem reactions with auto‐tandem catalysis are effective for simplifying organic synthesis. However, some of the reported reactions were established based on the use of well‐designed substrate with complex structure. In some cases, owing to the existence of a big gap between each catalytic cycle, it is hard to bind all the individual reaction steps to be a peaceful sequence. To enrich the diversity and also to strengthen the practical usefulness of the methodology developed by auto‐tandem catalysis, an additive‐like component was added to induce acid‐acid‐catalyzed tandem reaction. During the reaction, the additive‐like component acted either as an activator to increase the reactivity of the starting material or a hided reagent to enable successful transformation of the intermediate. Many novel tandem reactions were established in a one‐pot manner with the aid of this strategy. Importantly, this strategy not only allows the use of simple and commercially available chemicals as substrates, but also possesses multiple merits, such as simplifying operation, lowering waste generation and enhancing synthetic efficiency and atom‐economy. A summarization of the additive‐like component‐induced auto‐tandem catalysis with an acid catalyst was given in this review, in which many acid‐acid‐catalyzed tandem reactions were discussed. The reported additive‐like components were classified as three types: oxidative type, reductive type and neutral type depending on their mechanisms in assisting the establishment of acid‐acid‐catalyzed tandem reactions. Many examples were collected and analyzed from the viewpoints of simplifying the synthesis and manifesting their superior and distinct functionalities of the additives. A perspective of this concept was also given at the end of this review.     

Nickel‐Catalyzed Esterification of Aliphatic Amides

Recent studies have demonstrated that amides can be used in nickel‐catalyzed reactions that lead to cleavage of the amide C?N bond, with formation of a C?C or C?heteroatom bond. However, the general scope of these methodologies has been restricted to amides where the carbonyl is directly attached to an arene or heteroarene. We now report the nickel‐catalyzed esterification of amides derived from aliphatic carboxylic acids. The transformation requires only a slight excess of the alcohol nucleophile and is tolerant of heterocycles, substrates with epimerizable stereocenters, and sterically congested coupling partners. Moreover, a series of amide competition experiments establish selectivity principles that will aid future synthetic design. These studies overcome a critical limitation of current Ni‐catalyzed amide couplings and are expected to further stimulate the use of amides as synthetic building blocks in C?N bond cleavage processes.     

Acid‐Catalyzed Oxidative Radical Addition of Ketones to Olefins

Based on a mechanistic study, we have discovered a Brønsted acid catalyzed formation of ketone radicals. This is believed to proceed via thermally labile alkenyl peroxides formed in situ from ketones and hydroperoxides. The discovery could be utilized to develop a multicomponent radical addition of unactivated ketones and tert‐butyl hydroperoxide to olefins. The resulting γ‐peroxyketones are synthetically useful intermediates that can be further transformed into 1,4‐diketones, homoaldol products, and alkyl ketones. A one‐pot reaction yielding a pharmaceutically active pyrrole is also described.     

Solvent Effects in Acid‐Catalyzed Biomass Conversion Reactions

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid‐catalyzed conversion of xylose into furfural. A solvent of particular importance is γ‐valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2‐propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pK_a values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H‐mordenite and H‐beta.     

N‐Heterocyclic‐Carbene‐Catalyzed Synthesis of 2‐Aryl Indoles

A convergent and efficient transition‐metal‐free catalytic synthesis of 2‐aryl‐indoles has been developed. The interception of a highly reactive and transient aza‐ortho‐quinone methide by an acyl anion equivalent generated through N‐hetereocyclic carbene catalysis is central to this successful strategy. High yields and a wide scope as well as the streamlined synthesis of a kinase inhibitor are reported.     

Lewis Base Catalyzed Stereo‐ and Regioselective Bromocyclization

Oxygen‐ and nitrogen‐containing heterocyclic compounds are widely recognized as key components in many natural products and biologically relevant molecules, but often the problem comes down to methodologies in synthesizing them. Halocyclization of olefinic substrates is a promising strategy in the construction of O‐ and N‐heterocyclic compounds, which further signifies the development of their asymmetric variants. Over the past years, our group has been devoted to this particular area of asymmetric electrophilic halocyclization with chalcogen‐containing molecules as catalysts. In this account, the main focus is on the development of our novel chiral catalysts and applications derived from the reaction products.     

Selectivity Control in Gold‐Mediated Esterification of Methanol

The Midas touch : The low‐temperature transformation of methanol to methyl formate, formaldehyde, and formic acid is promoted by atomic oxygen adsorbed on metallic gold (see picture). The reactions occur with O‐containing Au nanoparticles formed on Au(111) upon oxidation with ozone at 200 K; the facile esterification to methyl formate occurs well below room temperature.

     

Brönsted酸性离子液体催化酯化反应研究

合成了以2-吡咯烷酮和N-甲基咪唑为阳离子([Hnhp]＋和[Hmim]＋), , 和 为阴离子的一系列Brönsted酸性离子液体. 考察了这些离子液体的热稳定性和酸性. 以乙酸和异戊醇酯化合成乙酸异戊酯的反应考察了不同离子液体分别在不分水与分水条件下的催化效果, 结果表明, 不分水时, 当醇/酸/[Hnhp]HSO4物质的量比为1.2∶1∶0.2, 100 ℃下回流反应2 h, 酯收率可达93.6%, 反应结束后[Hnhp]HSO4体系可以顺利分相, [Hnhp]BF4则不能; 分水时, [Hnhp]BF4可与酯自动分相, 当醇/酸/[Hnhp]BF4物质的量比为1.2∶1∶0.01, 120 ℃下回流反应1.5 h时, 酯收率可达96.8%, 比相同条件下[Hnhp]HSO4的略高. 这两种体系中的离子液体均具有良好的重复使用性能. 实验中还探讨了不同离子液体的酸性和催化酯化反应后与酯产物的分相效果对其催化活性的影响, 结果表明, 离子液体的酸性和与酯的不可混溶性对其在不同体系中酯化反应的催化活性有不同程度的影响. 此外, 在上述不分水酯化条件(醇∶酸∶催化剂物质的量比均为1.2∶1∶0.2, 100 ℃油浴)下回流浸渍6 h比较离子液体[Hnhp]HSO4/BF4, [Hmim]HSO4/BF4和硫酸对奥氏体316不锈钢的腐蚀性, 测得离子液体腐蚀率比硫酸低; 除了[Hnhp]BF4, 离子液体[Hnhp]HSO4, [Hmim]HSO4和[Hmim]BF4的腐蚀性呈现随酸性递减而下降的趋势. 所测离子液体中[Hnhp]BF4腐蚀性最高. [Hnhp]BF4和硫酸中试样的腐蚀率分别为20.1和41.8 g/(m2•h).     

An Acid‐Catalyzed Fragmentation Reaction of a Triamine‐Linked Acridine Dimer

An acid‐catalyzed cleavage of the C‐N^? bond from N^?‐(2,3,4,5‐tetrahydroxyvaleryl) substituted side chain and/or its acetonide form of a triamine‐linked acridine dimer is de scribed. An envisaged multi‐neighboring group‐assisted solvolysis reaction mechanism is proposed.     

Direct Observation of Unstable Reaction Intermediates by Acid‐Base Complex Formation

The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X‐ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single‐crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid‐base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid‐base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X‐ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid‐base complex crystals with various alkylammonium cations. The formation of acid‐base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X‐ray techniques.     

Following Solid‐Acid‐Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase—Zeolite‐Catalyzed Conversion of Cyclohexanol in Water

A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The ¹³C spectra show that dehydration of 1‐¹³C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the ¹³C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐¹³C‐cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2‐hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl‐1‐cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100‐fold faster per proton.     

Pd‐Colloids‐Catalyzed/Ag2O‐Oxidized General and Selective Esterification of Benzylic Alcohols

Palladium colloids obtained from the degradation of Hermann–Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative‐esterification successfully.     

高氯酸锂促进的固体酸催化酯化反应

将二(三氟甲基磺酰)亚胺镱(Ⅲ)[Yb(NTf2)3]负载于NKC-9树脂上得到一种催化活性更高的酯化固体酸催化剂,发现高氯酸锂能够显著加速固体酸催化剂酯化反应速度,在不分水,相对于苯甲酸负载树脂用量30 wt%,Yb(NTf2)3用量0.8mol%,LiClO4用量58 mol%,n(苯甲酸):n(乙醇)=1:7的条件下,2 h内即可使苯甲酸与乙醇的直接酯化反应进行完全.同时研究了负载量、温度、高氯酸锂用量对苯甲酸酯化反应的影响.     

Direct Three‐Component Synthesis of α‐Cyano Acrylates Involving Cascade Knoevenagel Reaction and Esterification

A direct three‐component approach has been developed for the synthesis of α‐cyano acrylates starting from aldehydes, alcohols and α‐cyano acetamide by employing cyanuric chloride as an organocatalyst. A class of structurally diverse α‐cyano acrylates have been provided with good to excellent yields via the cascade transformation of Knoevenagel condensation and amide esterification.     

CO/C‐H as an Acylating Reagent: A Palladium‐Catalyzed Aerobic Oxidative Carbonylative Esterification of Alcohols

A palladium‐catalyzed oxidative carbonylative esterification of a variety of functionalized alcohols under base‐ and ligand‐free conditions has been demonstrated. A CO/olefin combination was utilized as the acylating reagent with O₂ as a benign oxidant. Notably, the scope of the substrate alcohols has been greatly broadened.     

Cooperative Catalytic Reactions Using Distinct Transition‐Metal Catalysts: Ruthenium‐ and Copper‐Catalyzed Enantioselective Propargylic Alkylation

The enantioselective propargylic alkylation of propargylic alcohols with β‐ketoesters in the presence of a thiolate‐bridged diruthenium complex and a copper complex as co‐catalyst affords the corresponding propargylic alkylated products in excellent yields as a mixture of two diastereoisomers with high enantioselectivity (up to 95 % enantiomeric excess (ee)). The findings reported herein not only open up a new type of enantioselective propargylic substitution reaction, but also a new aspect of cooperative catalytic reactions using distinct transition metals to realize a useful transformation that cannot be achieved by a single catalyst.