Fullerenyl boronic esters: ferric perchlorate-mediated synthesis and functionalization

Fullerenyl boronic esters have been prepared by a ferric perchlorate-promoted reaction of [60]fullerene with various arylboronic acids. The obtained fullerenyl boronic esters could undergo further functionalization with diols to afford C(60)-fused dioxane/dioxepane derivatives. A possible reaction mechanism for the formation of fullerenyl boronic esters has been proposed.     

A synthesis of biaryl ketones via the C–S bond cleavage of thiol ester by a Cu/Ag salt

We report the synthesis of biaryl ketones via an unprecedented copper/silver catalyzed acylative cross-coupling of thiol esters with either an arylboronic acid or a potassium aryltrifluoroborate. This new method proceeds without a requisite Pd-catalyst and Cu(I)TC mediator, and is efficient, versatile, operationally simple, and accommodating functionally diverse thiol esters, arylboronic acids, and potassium aryltrifluoroborates.     

Base-free oxidative homocoupling of arylboronic esters

Base-free oxidative homocoupling reaction of arylboronic esters has been found to proceed using a catalytic amount of a palladium-1,3-bis(diphenylphosphino)propane (DPPP) complex under an oxygen atmosphere, affording a variety of biaryls in modest to excellent yields. Even arylboronic esters bearing a base-sensitive functional group are applicable to the reaction.     

Pd/TEMPO-catalyzed electrooxidative synthesis of biaryls from arylboronic acids or arylboronic esters

A facile electrooxidative method for synthesizing biaryls from arylboronic acids or arylboronic esters is described. In the presence of a catalytic amount of Pd(OAc)₂ and TEMPO, the electrooxidation of arylboronic acids or arylboronates gave the corresponding biaryls in moderate to excellent yields.     

Ligand‐Enabled Catalytic C?H Arylation of Aliphatic Amines by a Four‐Membered‐Ring Cyclopalladation Pathway

A palladium‐catalyzed C H arylation of aliphatic amines with arylboronic esters is described, proceeding through a four‐membered‐ring cyclopalladation pathway. Crucial to the successful outcome of this reaction is the action of an amino‐acid‐derived ligand. A range of hindered secondary amines and arylboronic esters are compatible with this process and the products of the arylation can be advanced to complex polycyclic molecules by sequential C H activation reactions.     

Ligand‐Enabled Catalytic CH Arylation of Aliphatic Amines by a Four‐Membered‐Ring Cyclopalladation Pathway

A palladium‐catalyzed C? H arylation of aliphatic amines with arylboronic esters is described, proceeding through a four‐membered‐ring cyclopalladation pathway. Crucial to the successful outcome of this reaction is the action of an amino‐acid‐derived ligand. A range of hindered secondary amines and arylboronic esters are compatible with this process and the products of the arylation can be advanced to complex polycyclic molecules by sequential C? H activation reactions.     

Nouvelle méthode de synthèse d’acides et d’esters arylboroniques par électroréduction de dérivés aromatiques halogénés en présence d’agents boratants

Novel synthesis of arylboronic acids and esters by electroreduction of aromatic halides in the presence of borating agents. A novel strategy for the one-step synthesis of arylboronic acids and esters by an electrochemical coupling reaction is described. It is based on the reductive coupling between the aromatic halides and a borating agent (trialkyl borate or pinacolborane). The reactions are carried out in DMF or THF with the use of sacrificial magnesium or aluminium anodes in a single-compartment cell. Arylboronic acids and esters are obtained with moderate-to-good isolated yields. To cite this article: C. Laza, E. Duñach, C. R. Chimie 6 (2003).     

A mild conversion of arylboronic acids and their pinacolyl boronate esters into phenols using hydroxylamine

Hydroxylamine was found to be a mild reagent for conversion of arylboronic acids and their pinacolyl boronate esters into phenols. This procedure works on most arylboronic acids at room temperature, yielding phenols in moderate to good yields, and efficiently on arylboronates also yielding phenols in good yields.     

Homocoupling of arylboronic acids catalyzed by simple gold salts

A range of arylboronic acids undergo a homocoupling reaction in the presence of catalytic amount of gold salts to yield symmetrical biaryls. Alkenylboronic acids, arylboronic esters, and arylborates also participate in the gold-catalyzed homocoupling reaction.     

Reduction of aromatic and aliphatic keto esters using sodium borohydride/MeOH at room temperature: a thorough investigation

Reduction of keto esters is a valuable alternative to produce diols. Sodium borohydride/MeOH system at room temperature and short reaction time efficiently reduced α, β, γ, and δ-keto esters having α-keto esters as the most reactive. The ester functionality was reduced effectively due to the presence of oxo group that somehow facilitates the formation of ring intermediate. As expected, the chemoselective experiments showed that ester functionality was not reduced using this system. This study presents a simple, easy, and benign reduction process of various keto esters to its corresponding diols.     

Facile synthesis of arylboronic esters by palladacycle-catalyzed bromination of 2-arylbenzoxazoles and subsequent borylation of the brominated products

An efficient and facile synthesis of arylboronic esters bearing the benzoxazole moiety has been described using a new family of palladacycle: cyclopalladated ferrocenylimines as the catalysts. This reaction includes two concessive steps: bromination of 2-arylbenzoxazoles and subsequent borylation. The bromination of para-C-H bond was an electrophilic substitution process by using NBS as the brominating reagent, and the brominated products were determined by HMBC (¹H-detected heteronuclear multiple bond correlation) spectra. Particularly, the borylation step could be carried out successively only after removal of the solvent to afford the arylboronic esters in moderate to good yields.     

Synthesis of substituted 2-cyanoarylboronic esters

The synthesis of substituted 2-cyanoarylboronic esters is described via lithiation/in situ trapping of the corresponding methoxy-, trifluoromethyl-, fluoro-, chloro-, and bromobenzonitriles. The crude arylboronic esters were obtained in high yields and purities and with good regioselectivities.     

Substituent Effects on Oxidation‐Induced Formation of Quinone Methides from Arylboronic Ester Precursors

A series of arylboronic esters containing different aromatic substituents and various benzylic leaving groups (Br or N⁺Me₃Br^?) have been synthesized. The substituent effects on their reactivity with H₂O₂ and formation of quinone methide (QM) have been investigated. NMR spectroscopy and ethyl vinyl ether (EVE) trapping experiments were used to determine the reaction mechanism and QM formation, respectively. QMs were not generated during oxidative cleavage of the boronic esters but by subsequent transformation of the phenol products under physiological conditions. The oxidative deboronation is facilitated by electron‐withdrawing substituents, such as aromatic F, NO₂, or benzylic N⁺Me₃Br^?, whereas electron‐donating substituents or a better leaving group favor QM generation. Compounds containing an aromatic CH₃ or OMe group, or a good leaving group (Br), efficiently generate QMs under physiological conditions. Finally, a quantitative relationship between the structure and activity has been established for the arylboronic esters by using a Hammett plot. The reactivity of the arylboronic acids/esters and the inhibition or facilitation of QM formation can now be predictably adjusted. This adjustment is important as some applications may benefit and others may be limited by QM generation.     

The Cu-catalyzed C–P coupling of phosphonate esters with arylboronic acids

Copper-catalyzed C–P cross coupling of phosphonate esters with arylboronic acids has been developed. The reaction provided an efficient method for aryl phosphonates under mild conditions.     

Practical one-pot stereospecific preparation of vicinal and 1,3-diols

A facile one-pot synthesis providing vicinal diols and 1,3-diols in >95% stereoisomeric purity from commercially available enantiopure hydroxy esters has been developed. The esters were reduced with DIBALH and alkylated in situ with 4-pentenylmagnesium bromide, which after workup generated the title diols as diastereomeric pairs. These pairs were easily separated by preparative chromatography, affording products with retained stereoisomeric purity from the starting materials. This method represents an expedient preparation of many common natural products, such as cerambycid beetle pheromones and intermediates towards bicyclic acetal bark beetle pheromones.     

Synthesis of Functionalized o‐, m‐, and p‐Terphenyl Derivatives by Consecutive Cross‐Coupling Reactions of Triazene‐Substituted Arylboronic Esters

Triazene‐substituted arylboronic esters were prepared readily from the corresponding aryl magnesium derivatives and shown to function as a new class of donor–acceptor‐substituted coupling reagents. The selective functionalization of these aromatic derivatives led to a wide variety of terphenyl derivatives in which the original bifunctional unit (often further substituted with another functional group) formed the central aromatic ring. The functionalized terphenyl derivatives were formed in two efficient cross‐coupling steps from the triazene‐substituted boronic esters: Suzuki cross‐coupling with an aryl halide was followed by BF₃?OEt₂‐induced palladium‐catalyzed coupling of the diazonium salt generated in situ from the triazene with an arylboronic acid.     

Synthetic protocol for diarylethenes through Suzuki-Miyaura coupling

The synthesis of a variety of diarylethenes through the Suzuki-Miyaura coupling reaction of 1,2-dichlorohexafluorocyclopentene with arylboronic acids and esters has been developed. Thiophenes with various substituents such as cyano and ester functionalities can be incorporated.     

A Comparative Study of the Relative Stability of Representative Chiral and Achiral Boronic Esters Employing Transesterification

A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters, pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3-diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C ₂-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol.     

Rhodium-catalyzed Heck-type reaction of arylboronic acids with alpha,beta-unsaturated esters: tuning beta-hydrogen elimination vs. hydrolysis of alkylrhodium species

The elusive rhodium-catalyzed Heck-type coupling of arylboronic acids with alpha,beta-unsaturated esters is effected using rhodium chloride as catalyst, indicating the hydrolysis of Rh-C bond could be finely tuned by the steric environment around rhodium.     

Synthesis of tertiary benzamides via Pd-catalyzed coupling of arylboronic esters and carbamoyl chlorides

Ortho-substituted arylboronic esters are efficiently coupled with carbamoyl chlorides under Pd-catalysis to give tertiary benzamides.