Chemoselective Boronic Ester Synthesis by Controlled Speciation

Control of boronic acid solution speciation is presented as a new strategy for the chemoselective synthesis of boronic esters. Manipulation of the solution equilibria within a cross‐coupling milieu enables the formal homologation of aryl and alkenyl boronic acid pinacol esters. The generation of a new, reactive boronic ester in the presence of an active palladium catalyst also facilitates streamlined iterative catalytic C? C bond formation and provides a method for the controlled oligomerization of sp²‐hybridized boronic esters.     

A Highly Efficient Copper‐Mediated Radioiodination Approach Using Aryl Boronic Acids

A convenient and quantitative radioiodination method by copper‐mediated cross‐coupling of aryl boronic acids was developed. The mild labeling conditions, ready availability of the boronic acid substrate, simple operation, broad functional group tolerance and excellent radiochemical yield (RCY) make this a practical strategy for radioiodine labeling without further purification.     

Synthesis of Aldehydes by Organocatalytic Formylation Reactions of Boronic Acids with Glyoxylic Acid

Reported herein is a conceptually novel organocatalytic strategy for the formylation of boronic acids. New reactivity is engineered into the α‐amino‐acid‐forming Petasis reaction occurring between aryl boronic acids, amines, and glyoxylic acids to prepare aldehydes. The operational simplicity of the process and its ability to generate structurally diverse and valued aryl, heteroaryl, and α,β‐unsaturated aldehydes containing a wide array of functional groups, demonstrates the practical utility of the new synthetic strategy.     

Keteniminium‐Driven Umpolung Difunctionalization of Ynamides

A three‐component Pd‐catalyzed coupling of ynamides, aryl diazonium salts, and aryl boronic acids for the synthesis of novel triaryl‐substituted enamides is described. This transformation represents the first example of an umpolung regioselective unsymmetrical syn‐1,2‐diarylation/aryl‐olefination of ynamides. The aryl moieties of the diazonium salt (electrophile) and boronic acid (nucleophile) are explicitly incorporated in the electrophilic α‐ and nucleophilic β‐position, respectively, of the ynamide, resulting in a single isomer of the N‐bearing tetrasubstituted olefin. The scope is broad (68 examples), showing excellent functional‐group tolerance. DFT calculations substantiate the rationale of the mechanistic cycle and the regioselectivity. The chemoselectivity and synthetic potential of the enamide products were also studied.     

迭代Suzuki偶联反应合成全氟环丁基芳基醚齐聚物的研究

对迭代Suzuki偶联反应合成全氟环丁基芳基醚齐聚物的方法进行了研究, 并合成了全氟环丁基芳基醚齐聚物. 首先从对溴苯酚出发, 合成了含有一个全氟环丁基芳基醚结构单元的中间体3. 芳基硼酸与中间体3进行Suzuki偶联反应, 得到了含有一个全氟环丁基芳基醚结构单元的硼酸. 重复与中间体3进行Suzuki偶联反应, 从而合成了全氟环丁基芳基醚二聚体和三聚体. 最后通过热环化二聚反应合成了全氟环丁基芳基醚三聚体、五聚体和七聚体.     

Traceless Rhodium‐Catalyzed Hydroacylation Using Alkyl Aldehydes: The Enantioselective Synthesis of β‐Aryl Ketones

A one‐pot three‐step sequence involving Rh‐catalyzed alkene hydroacylation, sulfide elimination and Rh‐catalyzed aryl boronic acid conjugate addition gave products of traceless chelation‐controlled hydroacylation employing alkyl aldehydes. The stereodefined β‐aryl ketones were obtained in good yields with excellent control of enantioselectivity. Good variation of all three reaction components is possible.     

Rhodium‐Catalyzed Addition of Aryl Boronic Acids to 2,2‐Disubstituted Malononitriles

β‐Ketonitriles bearing a quaternary carbon at the 2‐position were prepared through Rh‐catalyzed addition of aryl boronic acids to 2,2‐disubstituted malononitriles. In contrast to the previously described transnitrilative cyanation of aryl boronic acids with dialkylmalononitriles, the present reaction avoids retro‐Thorpe collapse of the intermediate addition product through the use of a milder base. The reaction was amenable to a variety of aryl boronic acids and disubstituted malononitriles, providing a diverse array of β‐ketonitriles. The products could be further derivatized to valuable chiral α,α‐disubstituted‐β‐aminonitriles through addition reactions to the corresponding N ‐tert ‐butanesulfinyl imines.     

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.     

Facile synthesis of 2-bromo-3-fluorobenzonitrile: an application and study of the halodeboronation of aryl boronic acids

A scaleable synthesis of 2-bromo-3-fluorobenzonitrile via the NaOMe-catalyzed bromodeboronation of 2-cyano-6-fluorophenylboronic acid was developed. The generality of this transformation was demonstrated through the halodeboronation of a series of aryl boronic acids. Both aryl bromides and aryl chlorides were formed in good to excellent yields when the corresponding aryl boronic acid was treated with 1,3-dihalo-5,5-dimethylhydantoin and 5 mol % NaOMe.     

In Situ Formation of Polymeric Nanoassemblies Using an Efficient Reversible Click Reaction

Polymer–drug conjugates are promising as strategies for drug delivery, because of their high drug loading capacity and low premature release profile. However, the preparation of these conjugates is often tedious. In this paper, we report an efficient method for polymer–drug conjugates using an ultrafast and reversible click reaction in a post‐polymerization functionalization strategy. The reaction is based on the rapid condensation of boronic acid functionalities with salicylhydroxamates. The polymer, bearing the latter functionality, has been designed such that the reaction with boronic acid bearing drugs induces an in situ self‐assembly of the conjugates to form well‐defined nanostructures. We show that this method is not only applicable for molecules with an intrinsic boronic acid group, but also for the other molecules that can be linked to aryl boronic acids through a self‐immolative linker. The linker has been designed to cause traceless release of the attached drug molecules, the efficiency of which has been demonstrated through intracellular delivery.     

Copper‐Catalyzed Cross‐Coupling of Boronic Esters with Aryl Iodides and Application to the Carboboration of Alkynes and Allenes

Copper‐catalyzed Suzuki–Miyaura‐type cross‐coupling and carboboration processes are reported. The cross‐couplings function well with a variety of substituted aryl iodides and aryl boronic esters and allows for orthogonal reactivity compared to palladium‐catalyzed processes. The carboboration method includes both alkynes and allenes and provides access to highly substituted and stereodefined vinyl boronic esters. The alkyne carboboration method is highlighted in the simple one‐pot synthesis of Tamoxifen.     

Copper activation of boronic acids: factors affecting reactivity

The generation of nucleophiles from the combination of aryl boronic acids and catalytic amounts of copper salt allows a reactivity distinct from other organometallic species, such as organolithiums or Grignard reagents. Here we examine how the electronic and steric properties of the boronic acid affect the formation of active nucleophiles and their subsequent reactivity with iminium‐type compounds, showing that electron‐rich substrates display reduced reactivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Enantiospecific Synthesis of ortho‐Substituted 1,1‐Diarylalkanes by a 1,2‐Metalate Rearrangement/anti‐SN2′ Elimination/Rearomatizing Allylic Suzuki–Miyaura Reaction Sequence

The one‐pot sequential coupling of benzylamines, boronic esters, and aryl iodides has been investigated. In the presence of an N‐activator, the boronate complex formed from an ortho‐lithiated benzylamine and a boronic ester undergoes stereospecific 1,2‐metalate rearrangement/anti‐S_N2′ elimination to form a dearomatized tertiary boronic ester. Treatment with an aryl iodide under palladium catalysis leads to rearomatizing γ‐selective allylic Suzuki–Miyaura cross‐coupling to generate 1,1‐diarylalkanes. When enantioenriched α‐substituted benzylamines are employed, the corresponding 1,1‐diarylalkanes are formed with high stereospecificity.     

Oxidative cross-coupling of allyl(trimethyl)silanes with aryl boronic acids by palladium catalysis

The first oxidative cross-coupling of allylsilanes with aryl boronic acids has been developed by palladium catalysis. The reaction between β-substituted allyl(trimethyl)silanes and a wide range of aryl boronic acids afforded allylarenes in moderate to good yields and excellent selectivity. On the basis of experimental results and literature reports, it was suggested that the reaction might start from transmetalation of aryl boronic acid with AgOAc followed by transmetalation with Pd(II) to give an arylpalladium acetate complex as a key intermediate. This intermediate underwent either electrophilic addition/desilylation or transmetalation with allylsilane and subsequent reductive elimination to give the final product.     

Visible‐Light‐Mediated Chan–Lam Coupling Reactions of Aryl Boronic Acids and Aniline Derivatives

The copper(II)‐catalyzed aerobic oxidative coupling reaction between aryl boronic acids and aniline derivatives was found to be improved significantly under visible‐light‐mediated photoredox catalysis. The substrate scope of this oxidative Chan–Lam reaction was thus expanded to include electron‐deficient aryl boronic acids as viable starting materials.     

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

We report herein the use of a dual catalytic system comprising a Lewis base catalyst such as quinuclidin‐3‐ol or 4‐dimethylaminopyridine and a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react with electron‐deficient olefins via radical addition to efficiently form C−C coupled products in a redox‐neutral fashion. The Lewis base catalyst was shown to form a redox‐active complex with either the boronic esters or the trimeric form of the boronic acids (boroxines) in solution.     

CuI-catalyzed direct synthesis of diaryl thioethers from aryl boronic acids and arylsulfonyl chlorides

A CuI-catalyzed direct coupling of aryl boronic acids with arylsulfonyl chlorides for the preparation of diaryl thioethers was developed. The reaction is initiated by a PPh₃ reduction of the arylsulfonyl chloride, followed by a CuI-catalyzed C–S coupling with an aryl boronic acid. Various arylsulfonyl chlorides can directly serve as a sulfur source in this mild and efficient reaction giving the desired products in moderate to good yields. Moreover, this practical method has also been applied to the thioetherification of aryl iodides and acetylacetones.     

Heck-type coupling vs. conjugate addition in phosphine-rhodium catalyzed reactions of aryl boronic acids with alpha,beta-unsaturated carbonyl compounds: a systematic investigation

The competition between Heck-type coupling and conjugate addition in phosphine-rhodium catalyzed reactions of aryl boronic acids with alpha,beta-unsaturated carbonyls has been systematically investigated in a toluene-H(2)O biphasic system. Aside from the intrinsic nature of rhodium and the enolization of carbonyls, the phosphine supporting ligand on rhodium, the ratio of aryl boronic acid to alpha,beta-unsaturated carbonyl and the pH value of the aqueous phase were found to affect the competition significantly. Highly selective rhodium-based catalyst systems have therefore been developed for both Heck-type coupling and conjugate addition by synergistically tuning the supporting ligand, the boronic acid to olefin ratio and other reaction conditions. Conjugate addition with selectivity >99% and Heck-type coupling with selectivity of up to 100%, 98% and 84% for acrylates, acrylamides and methyl vinyl ketone, respectively, could be achieved in the rhodium-catalyzed reactions of aryl boronic acids with alpha,beta-unsaturated carbonyls using the corresponding optimized rhodium-based catalyst systems.     

Direct Cross‐Couplings of Propargylic Diols

[Pd(PPh₃)₄] catalyzes a Suzuki–Miyaura‐like twofold cross‐coupling sequence between underivatized propargylic diols and either aryl or alkenyl boronic acids to furnish highly substituted 1,3‐dienes. Thus, 2,3‐diaryl‐1,3‐butadienes and their dialkenic congeners ([4]dendralenes) are delivered in a (pseudo)halogen‐free, single‐step synthesis which supersedes existing methods. Allenols are also readily formed. Treatment of these single‐ and twofold cross‐coupled products with acid leads to remarkably short syntheses of highly‐substituted benzofulvenes and aryl indenes, respectively.     

Direct Access to α,α‐Difluoroacylated Arenes by Palladium‐Catalyzed Carbonylation of (Hetero)Aryl Boronic Acid Derivatives

A palladium‐catalyzed carbonylative coupling of (hetero)aryl boronates or boronic acid salts with carbon monoxide and α‐bromo‐α,α‐difluoroamides and bromo‐α,α‐difluoroesters is described herein. The method is useful for the synthesis of a diverse selection of (hetero)aryl α,α‐difluoro‐β‐ketoamides and α,α‐difluoro‐β‐ketoesters, which are useful building blocks for the generation of functionalized difluoroacylated and difluoroalkyl arenes. The method could be further extended to a one‐pot protocol for the formation of difluoroacetophenones.