Palladium/Brønsted Acid‐Catalyzed α‐Allylation of Aldehydes with Allylic Alcohols

A simple, highly efficient, and readily scalable direct α‐allylation of aldehydes with allylic alcohols that is co‐catalyzed by palladium and a Brønsted acid has been developed.     

Mild and Efficient Allylation of Aldehydes by using Copper Fluorapatite as Catalyst

A facile synthesis of homoallylic alcohols is achieved by the allylation of aldehydes with allylic metal reagents or allyl halides using copper fluorapatite (CuFAP) as catalyst under mild reaction conditions. A variety of aldehydes were converted to the corresponding homoallylic alchohols, demonstrating the versatility of the reaction.     

过渡金属催化下醛的烯丙基化反应研究进展

烯丙基醇在有机合成中是一类重要中间体,醛的烯丙基化反应是制备烯丙基醇的一类重要方法,其中过渡金属作为催化剂,在该领域获得了突飞猛进的发展。文章综述了近两、三年来在过渡金属催化下金属烯丙基试剂及其替代品与醛的烯丙基化反应研究进展。     

The Reductive Amination of Aldehydes and Ketones and the Hydrogenation of Nitriles: Mechanistic Aspects and Selectivity Control

This review deals with two of the most commonly used methods for the preparation of amines: the reductive amination of aldehydes and ketones and the hydrogenation of nitriles. There is a great similarity between these two methods, since both have the imine as intermediate. However, due to the high reactivity of this intermediate, primary, secondary and/or tertiary amines are obtained (often simultaneously). The relation of the selectivity to different substrate structures and reaction conditions is briefly summarised, the main focus being on the catalyst as it is the most significant factor that governs the selectivity. Different mechanisms are discussed with the view to correlate the structure of the catalyst and, more particularly, the nature of the metal and the support with selectivity. The crucial point is the presumed location of the condensation and hydrogenation steps.     

Efficient Allylation of Nucleophiles Catalyzed by a Bifunctional Heterogeneous Palladium Complex‐Tertiary Amine System

We demonstrate the synergistic catalysis of a silica‐supported diaminopalladium complex and a tertiary amine (SiO₂/diamine/Pd/NEt₂) as well as synthetic scope of the Tsuji–Trost reaction of 1,3‐dicarbonyls, phenols, and carboxylic acids with allyl carbonate and acetates. The synergistic catalysis of SiO₂/diamine/Pd/NEt₂ exhibited wide applicability and high activity for the Tsuji–Trost reaction. For example, the reaction of ethyl 3‐oxobutanate with allyl methyl carbonate afforded the allylated product in >99% yield at 70 °C for 5 h. The yield of allylated products was 26% for SiO₂/diamine/Pd, without immobilization of the tertiary amine group. In the reaction of 1.0 mmol of ethyl 3‐oxobutanate using 0.60 μmol of Pd in SiO₂/diamine/Pd/NEt₂, the turnover number (TON) of Pd reached up to 1070 within 24 h. Phenols with electron‐withdrawing groups, such as nitro and chloro groups, on the para position resulted in high product yields. The SiO₂/diamine/Pd/NEt₂ catalyst was reusable at least 4 times without appreciable loss of its activity and selectivity in the reaction of p‐chlorophenol.     

Palladium‐Catalyzed Stereospecific Allylation of Nitroacetates with Enantioenriched Primary Allylic Amines

An unprecedented stereospecific allylation reaction of nitroacetates with enantioenriched primary allylic amines has been developed. A range of nitroacetates smoothly underwent allylation with enantioenriched primary allylic amines in the presence of a palladium catalyst and boric acid followed by one‐pot decarboxylation to afford structurally diverse homoallylic nitro compounds in good to excellent yields with excellent retention of configuration. On the other hand, the allylation followed by denitronation provided a facile synthetic route to optically active β‐chiral γ,δ‐unsaturated esters.

     

The Evolution of Decarboxylative Allylation: Overcoming pKa Limitations

Since early focus on development of the allylation of non-stabilized enolates, decarboxylative allylation has undergone tremendous evolution. This account describes the progression of decarboxylative allylation within the Tunge group with a focus on efforts to identify and overcome pK_a requirements that initially limited the carboxylates that would undergo decarboxylative allylation.     

The First Decarbonylative Coupling of Aldehydes and Norbornenes Catalyzed by Rhodium

The decarbonylative coupling of aldehydes and norbornene analogues was realized for the first time by using a rhodium(I) catalyst.     

A Simple Approach to Unsymmetric Atropoisomeric Bipyridine N,N′‐Dioxides and Their Application in Enantioselective Allylation of Aldehydes

The [2+2+2] cyclotrimerization of 1‐isoquinolinyl‐1,7‐octadiyne with benzonitrile catalyzed by CpCo(CO)₂ opened a new pathway for a synthesis of unsymmetrical axially chiral bipyridine N,N′‐dioxides. The N,N′‐dioxide 3a was found to be highly catalytically active and enantioselective for the asymmetric allylation of aldehydes with allyltrichlorosilane. The allylation took place with even 1 % of the catalyst with an enantioselectivity up to 87 % ee.     

Palladium‐Catalyzed Methoxycarbonylation of 1,3‐Butadiene: Catalysis and Mechanistic Studies

The palladium‐catalyzed methoxycarbonylation of 1,3‐butadiene to methyl 3‐pentenoate has been studied. Intermediates of the proposed catalytic cycle were synthesized and the elementary steps of the reaction have been investigated in detail. It is shown that the first step of the catalytic cycle, the formation of crotylpalladium complexes from 1,3‐butadiene, proceeds even at room temperature. Examination of the influence of different reaction parameters on product yield and selectivity demonstrate the importance of chelating phosphine ligands and benzoic acids as additive in order to get good results.     

Low‐Pressure Hydrogenation of Arenecarboxylic Acids to Aryl Aldehydes

A highly effective palladium catalyst has been developed that allows the selective hydrogenation of arenecarboxylic acids to the aryl aldehydes in the presence of pivalic anhydride already at 5 bar hydrogen pressure. With the new catalyst, diversely functionalized aromatic and heteroaromatic aldehydes are conveniently accessible from the corresponding carboxylic acids in a single reaction step without any overreduction to the alcohols.     

Palladium on Carbon‐Catalyzed C−H Amination for Synthesis of Carbazoles and its Mechanistic Study

10% Palladium on carbon (10% Pd/C) successfully catalyzed the intramolecular C−H amination of various N‐mesylated 2‐aminobiphenyls in the presence of a catalytic amount of pyridine N‐oxide in heated dimethyl sulfoxide (DMSO) under an oxygen atmosphere to afford the corresponding N‐mesylcarbazoles. The reaction would proceed via a single‐electron transfer process based on its significant suppression by the addition of a single‐electron scavenger, tetracyanoquinodimethane (TCNQ), and the substituents on the aromatic rings of the substrate have an insignificant effect on the reaction progress.

     

High Atom Efficiency in Sc(OTf)3‐Catalyzed Allylation of Aldehydes with Tetraallyltin

The high atom efficiency was achieved through addition of Ac₂O in the Sc(OTf)₃‐catalyzed allylation of aldehyde with tetraallytin in a 4 : 1 molar ratio.     

A Chiral Bipyridyl Alcohol for Catalytic Enantioselective Nozaki–Hiyama–Kishi Allylation of Aldehydes and Ketones

A class of bipyridyl alcohol ligands has been developed. A catalyst synthesized using a chromium(II)‐ligand promotes the enantioselective Nozaki–Hiyama–Kishi (NHK) allylation of aldehydes and ketones with allylic halides. The allylation of various aromatic, α,β‐unsaturated, and aliphatic aldehydes and ketones produces the desired homoallylic alcohols in satisfactory yields (up to 98%) and high enantioselectivities (up to 99% ee). The present method can be applied widely and affords an efficient means of obtaining chiral homoallylic alcohols.

     

Stereocontrol in Palladium‐Catalyzed Propargylic Substitutions: Kinetic Resolution to give Enantioenriched 1,5‐Enynes and Propargyl Acetates

Kinetic resolution during the catalytic allyl‐propargyl cross‐coupling with chiral starting materials can be accomplished with a chiral palladium catalyst. These reactions offer ready access to enantiomerically enriched enyne products from simple, readily available starting materials.

     

Palladium‐Catalyzed Three‐Component Reaction of 3‐(Tri‐n‐ butylstannyl)allyl Acetates,Aldehydes, and Triorganoboranes: An Alternative to the Carbonyl Allylation Using α,γ‐Substituted Allylic Tin Reagents

A three‐component reaction of 3‐(tri‐n‐butylstannyl)allyl acetates, aldehydes, and triorganoboranes in the presence of a palladium‐Xantphos catalyst system predominately gave (E)‐anti‐homoallylic alcohols with high diastereoselectivity and good to high levels of alkene stereocontrol. An efficient chirality transfer was observed when an enantioenriched substrate was employed. The reaction was initiated by the formation of an allylic gem‐palladium/stannyl intermediate, which subsequently underwent allylation of the aldehyde by an allyltributyltin followed by a coupling reaction of the in‐situ‐generated (E)‐vinylpalladium acetate with the triorganoborane.

     

Tandem Catalysis: Access to Ketones from Aldehydes and Arylboronic Acids via Rhodium‐Catalyzed Addition/Oxidation

Direct cross‐coupling reactions of aromatic aldehydes with arylboronic acids afforded ketones in high yields and under mild conditions in the presence of a rhodium catalyst, acetone and a base. This new reaction, involving a formal aldehyde C H bond activation, is believed to proceed via a tandem process involving addition of the organometallic species to the aldehyde followed by oxidation by β‐hydride transfer.     

冷冻干燥法制备壳聚糖/粘土多孔微球负载钯催化剂的性能研究

利用冷冻干燥法制备得到了具有多孔结构的壳聚糖/粘土(蒙脱土)微球负载钯催化剂,催化剂孔径尺寸较大(100μm)。该催化剂应用于典型丙烯酸丁酯与芳基碘系物的Heck反应时,有较高的催化活性。加入适量粘土使壳聚糖分子链能有效地插入到蒙脱土的片层间,良好的插层结构有助于提升催化材料的耐热性和机械性能。相应地,壳聚糖/粘土多孔微球负载钯催化剂比纯壳聚糖负载钯多孔微球催化剂有更高的重复使用性能。