Visible‐Light‐Mediated Decarboxylative Radical Additions to Vinyl Boronic Esters: Rapid Access to γ‐Amino Boronic Esters

The synthesis of alkyl boronic esters by direct decarboxylative radical addition of carboxylic acids to vinyl boronic esters is described. The reaction proceeds under mild photoredox catalysis and involves an unprecedented single‐electron reduction of an α‐boryl radical intermediate to the corresponding anion. The reaction is amenable to a diverse range of substrates, including α‐amino, α‐oxy, and alkyl carboxylic acids, thus providing a novel method to rapidly access boron‐containing molecules of potential biological importance.     

路易斯碱-硼自由基促进的邻苯二甲酰亚胺类羧酸酯的Giese反应和Barton脱羧反应研究

邻苯二甲酰亚胺羧酸酯的自由基脱羧是产生碳自由基的一类重要方法. 开发了一类路易斯碱-硼自由基促进的邻苯二甲酰亚胺羧酸酯的自由基脱羧新方式, 产生的烷基自由基经过加成到缺电子烯烃上或者进一步还原得到Giese反应和Barton脱羧产物. 该反应条件温和, 适用范围广泛, 多种一级、二级和三级烷基羧酸包括具有生物活性的天然产物和药物分子都能够较好地适用, 为邻苯二甲酰亚胺羧酸酯的自由基脱羧提供了无过渡金属参与的具有普适性的新方式.     

Convenient Preparation of Cycloalkenyl Boronic Acid Pinacol Esters

A practical method for the preparation of cycloalkenyl boronic acid pinacol esters is described. These important synthetic intermediates are typically made using more expensive methods like transition metal-catalyzed borylation of alkenyl halides or triflates. In this work, they are obtained from the simple corresponding cycloalkanones, which are subjected to Shapiro reaction conditions followed by trapping with a borate ester. The requisite products are obtained in very good to excellent yields, and the reactions can be scaled up to multigram amounts. By providing a simple alternative to common methods that make use of expensive transition-metal catalysts and formation of sensitive intermediates, this convenient method will be useful for the synthesis of ring-containing partners for Suzuki–Miyaura cross-coupling and other reactions employing boronic esters as substrates.     

Decarboxylative Conjunctive Cross‐coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

The synthesis of complex alkyl boronic esters through conjunctive cross‐coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross‐coupling cascade of vinyl boronic esters. Excellent functional‐group tolerance is displayed, and application of a range of carboxylic acids, including secondary α‐amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross‐coupling was also applied to the synthesis of sedum alkaloids.     

Synthesis and Utility of Dihydropyridine Boronic Esters

When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products.     

Decarboxylative Benzylation of Aryl and Alkenyl Boronic Esters

The copper‐catalyzed decarboxylative benzylation of aryl and alkenyl boronic esters with electron‐deficient aryl acetates is reported. The oxidative coupling proceeds under mild, aerobic conditions and tolerates a host of potentially reactive electrophilic functional groups that would be problematic with traditional benzylation methods (aryl iodides and bromides, protic heteroatoms, aldehydes, Michael acceptors). A reaction pathway in which a benzylic nucleophile is generated by aryl acetate decarboxylation and in turn is intercepted by the catalyst to form diarylmethane products is supported by mechanistic studies.     

Decarboxylative Conjunctive Cross-coupling of Vinyl Boronic Esters using Metallaphotoredox Catalysis

The synthesis of complex alkyl boronic esters through conjunctive cross-coupling of vinyl boronic esters with carboxylic acids and aryl iodides is described. The reaction proceeds under mild metallaphotoredox conditions and involves an unprecedented decarboxylative radical addition/cross-coupling cascade of vinyl boronic esters. Excellent functional-group tolerance is displayed, and application of a range of carboxylic acids, including secondary α-amino acids, and aryl iodides provides efficient access to highly functionalized alkyl boronic esters. The decarboxylative conjunctive cross-coupling was also applied to the synthesis of sedum alkaloids.     

Reaction of Hydantoin with Boronic Acids

We have examined the reaction of hydantoin (=imidazolidine‐2,4‐dione) with (formylphenyl)boronic acids, where the addition of a boronic acid group is hoped to increase bioactivities. Addition of (2‐formylphenyl)boronic acid to hydantoin gave an unexpected azaborine compound, which presumably arises by initial formation of the (phenylmethylidene)hydantoin, with subsequent loss of H₂O to give the cyclized product. Reactions of (3‐formylphenyl)‐ and (4‐formylphenyl)boronic acids with hydantoin gave the corresponding [(Z)‐phenylmethylidene]hydantoins in good‐to‐excellent yields. Attempts to use (3‐formylthiophen‐2‐yl)boronic acid gave a product where the boronic acid group has been cleaved.     

Stereospecific Couplings of Secondary and Tertiary Boronic Esters

This Minireview highlights advances in the Suzuki–Miyaura cross‐coupling of secondary boron reagents for the creation of C? C bonds with control of stereochemistry. It also includes non‐transition‐metal coupling of secondary and tertiary boronic esters to electron‐rich aromatics.     

三乙烯二胺促进炔酸聚乙二醇酯与苯酚的加成反应研究

以单甲氧基聚乙二醇和2-丁炔酸为起始原料,制得2-丁炔酸聚乙二醇酯（1）;以异丙醇为溶剂,三乙烯二胺（DABCO）为催化剂,1与苯酚经Michael加成反应合成了苯酚的聚乙二醇化产物（2）,其结构经¹H NMR和FT-IR确证。在最优反应条件［n（苯酚）:n（1）: n（DABCO）=20:1:20,异丙醇0.5 mL,于室温反应12 h］下,2产率99%。     

新型糖氨基酸类化合物的合成研究

糖氨基酸(sugar amino acids, SAAs)是一类同时含有氨基和羧基的糖类衍生物, 具有糖和氨基酸的结构特征和化学反应特性, 常作为多功能合成砌块用于组合化学的研究、糖模拟物和多肽模拟物的构建等. 因此, 该类化合物的设计与合成受到国内外化学家的持续关注. 在本文中, 我们发展了一种简单、高效的合成新型糖氨基酸的方法, 从廉价易得的3,4,6-O-三乙酰基-D-葡萄糖烯和3,4,6-O-三乙酰基-D-半乳糖烯出发, 在硝酸铈铵(CAN)的作用下通过一步自由基加成反应分别得到2-C-二羧酸酯类化合物gluco-2和galacto-2, 再经过脱羧、脱乙酰、碘代、叠氮化钠取代和一锅法还原氨化反应, 以最短直线步骤6步实现了糖氨基酸gluco-7(总收率34%)和galacto-7(总收率19%)的合成. 所有合成的化合物均经过IR, ¹H NMR, ¹³C NMR和HRMS的表征.     

A General Approach to Deboronative Radical Chain Reactions with Pinacol Alkylboronic Esters

The generation of carbon‐centered radicals from air‐sensitive organoboron compounds through nucleohomolytic substitution at boron is a general method to generate non‐functionalized and functionalized radicals. Due to their reduced Lewis acidity, alkylboronic pinacol esters are not suitable substrates. We report their in situ conversion into alkylboronic catechol esters by boron‐transesterification with a substoichiometric amount of catechol methyl borate combined with an array of radical chain processes. This simple one‐pot radical‐chain deboronative method enables the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds through C?C bond formation using sulfonyl radical traps. The power of combining radical and classical boron chemistry is illustrated with a modular 5‐membered ring formation using a combination of three‐component coupling and protodeboronative cyclization.     

氧负离子与乙烯自由基反应的理论研究

在G3MP2B3理论水平下研究了氧负离子与乙烯自由基的反应机理. 反应入口势能面的刚性扫描显示: 对于不同的初始反应取向, 体系存在3种不同的反应机理, 分别对应直接脱水、插入反应和直接键合成中间体通道. 其中, 通过插入反应形成的富能中间体[CH2＝C—OH]－及键合中间体[CH2＝CHO]－都可以进一步经异构化和解离生成其它各种可能产物, 如C2H－＋H2O, OH－＋CH2C和 ＋CO产物通道. 基于计算得到的反应势垒的相对高度, 直接脱水反应显然是该反应体系最主要的产物通道, 同时我们还结合Mulliken电荷布居分析研究了其中涉及的电子交换过程. 由此, 计算结果证实了以往OH－与C2H2反应的实验研究结果. 此外, 还对比了该反应体系、氧原子与乙烯自由基、氧负离子与乙烯分子三个反应的不同机理.     

Photocatalytic Giese-Type Reaction with Alkylsilicates Bearing C,O-Bidentate Ligands

Herein, a photocatalytic Giese-type reaction with alkylsilicates bearing C,O-bidentate ligands as stable alkyl radical precursors has been reported. The alkylsilicates were prepared in one step from organometallic reagents. Not only primary, secondary, and tertiary alkyl radicals, but also elusive methyl radicals, could be generated by using the present reaction system. The generated radicals were trapped by electron-deficient olefins bearing various functional groups to give the desired alkyl adducts. The silicon byproduct can be recovered after the photoreaction. The radical generation process was investigated by theoretical calculations, which provided an insight into the facile generation of methyl radicals from methylsilicate bearing C,O-bidentate ligands.     

Reaction of Frustrated Lewis Pairs with Ketones and Esters

The frustrated Lewis pair (FLP) Mes₂PCH₂CH₂B(C₆F₅)₂ ( 1 ) reacts with an enolizable conjugated ynone by 1,4‐addition involving enolate tautomerization to give an eight‐membered zwitterionic heterocycle. The conjugated endione PhCO‐CH?CH‐COPh reacts with the intermolecular FLP tBu₃P/B(C₆F₅)₃ by a simple 1,4‐addition to an enone subunit. The same substrate undergoes a more complex reaction with the FLP 1 that involves internal acetal formation to give a heterobicyclic zwitterionic product. FLP 1 reacts with dimethyl maleate by selective overall addition to the C?C double bond to give a six‐membered heterocycle. It adds analogously to the triple bond of an acetylenic ester to give a similarly structured six‐membered heterocycle. The intermolecular FLP P(o‐tolyl)₃/B(C₆F₅)₃ reacts analogously with acetylenic ester by trans‐addition to the carbon–carbon triple bond. An excess of the intermolecular FLP tBu₃P/B(C₆F₅)₃, which contains a more nucleophilic phosphane, reacts differently with acetylenic ester examples, namely by O? C(alkyl) bond cleavage to give the {R‐CO₂[B(C₆F₅)₃]₂^?}[alkyl‐PtBu₃⁺] salts. Simple aryl or alkyl esters react analogously by using the borane‐stabilized carboxylates as good leaving groups. All essential products were characterized by X‐ray diffraction.     

Enantioselective Construction of Tertiary Boronic Esters by Conjunctive Cross‐Coupling

Catalytic enantioselective conjunctive cross‐coupling has been developed to construct tertiary alkylboronic esters. These reactions occur with good yield and enantioselectivity for a range of substrates. Mechanistic experiments reveal aspects of the catalytic cycle that allow hindered substrates to react without significant complicating side reactions.     

Room Temperature Coupling of Aryldiazoacetates with Boronic Acids Enhanced by Blue Light Irradiation

A visible-light-promoted photochemical protocol is reported for the coupling of aryldiazoacetates with boronic acids. This photochemical reaction shows great enhancement compared to the same protocol performed in the absence of light. Except for a few cases, the room temperature coupling in the dark (thermal process) generally does not work. When it does, it is likely to also involve free carbenes as key intermediates. Alternatively, photochemical reactions show a broad scope, can be performed under air and tolerate a wide variety of functional groups. Reaction-evolution monitoring, DFT calculations and control experiments have been used to evaluate the main aspects of this intricate mechanistic scenario. Biologically active molecules Adiphenine, Benactyzine and Aprophen have been prepared as examples of synthetic applications.