Gel-entrapped bases: A smart window for the ligand-free Suzuki–Miyaura cross-coupling reaction

A gel-entrapped base has been fabricated by using agarose (biopolymer), and tested in the Suzuki–Miyaura cross-coupling reaction in 95% ethanol. The developed environmentally benign polymer-supported base has low leaching and high stability for the Suzuki–Miyaura cross-coupling reaction to give high yield with green credit.     

A simple catalytic system based on PdCl2(CH3CN)2 in water for cross-coupling reactions using diazonium salts

Aryl–heteroaryl and heteroaryl–heteroaryl compounds are obtained through the Suzuki–Miyaura cross-coupling reactions between diazonium salts and potassium trifluoroborates using PdCl₂(CH₃CN)₂ as the catalyst in water and in the absence of any additive, ligand or base. In addition, the same mild catalytic system is effective for the Matsuda–Heck reaction between several monoolefins with aryldiazonium salts.     

Increasing appendage diversity on 3,4-dihydro-3-oxo-2H-1,4-benzoxazines via Aphos–Pd(OAc)2-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides

A library of 32 members of 3,4-dihydro-3-oxo-2H-1,4-benzoxazines has been synthesized from two substituted 2-aminophenols via microwave-assisted one-pot regioselective annulation of 2-bromoalkanoates and subsequent Suzuki–Miyaura cross-coupling of the chloro-substituted scaffolds. The latter transformation was carried out using our Aphos–Pd(OAc)₂ catalyst and the coupling of the aryl chlorides with arylboronic acids proceeded under mild reaction conditions at 60–80 °C in THF–H₂O (10:1) in the presence of K₃PO₄·3H₂O as the base to furnish the corresponding biaryl products in 80–98% yields.     

Regioselective Suzuki–Miyaura cross-coupling reactions of the bis(triflate) of 4,7-dihydroxycoumarin

Arylated coumarins were prepared by site-selective Suzuki–Miyaura cross-coupling reaction of the bis(triflate) of 4,7-dihydroxycoumarin. The reactions proceeded by initial attack to the sterically more hindered position, due to electronic reasons.     

Expedient BINOL derivative arylations

A dramatic improvement of our previous methodology based on a Suzuki–Miyaura cross-coupling to access 3,3′-disubstituted H₈-BINOLs using microwave heating is reported herein. These new conditions represent a large gain in term of atom-economy, reaction time, catalyst loading, and excess of reagents employed.     

Suzuki–Miyaura cross-coupling reaction of 1,2-oxaborol-2(5H)-ols with carboxylic anhydrides: a new method to furans

An efficient one-step method has been developed to construct furans via a Suzuki–Miyaura cross-coupling reaction of 1,2-oxaborol-2(5H)-ols with carboxylic anhydrides. In the presence of Pd(OAc)₂/PCy₃, the multi-substituted alkenylboron compounds could couple with anhydrides to obtain furans in moderate-to-good yields. The addition of bases promoted the coupling reaction, and the plausible reaction mechanism was proposed.     

Synthesis of 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophenes via cross-coupling reactions and sequential Lewis acid-catalyzed regioselective cycloaromatization of epoxide

Phenanthro[1,2-b:8,7-b′]dithiophene (PDT) was prepared via Suzuki–Miyaura or Negishi cross-coupling of a 2-thienylboron or -zinc compound with 1,4-dibromobenzene, followed by Lewis acid-catalyzed regioselective cycloaromatization of the epoxide. A series of 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophene (PDT) derivatives could also be synthesized in good yields by Suzuki–Miyaura coupling of the brominated PDT with alkylboranes by introducing linear alkyl substituents.     

Synthetic studies on polymaxenolides: model studies for constructing dihydropyran portion and synthesis of lower portion

With a goal of the total synthesis of polymaxenolide, the first hybrid marine natural product, the model studies for constructing the dihydropyran portion based on the originally proposed biosynthesis (C–C bond formation followed by dehydrative cyclization) and the synthesis of the lower portion (the C1–C3, C7–C17 portion) based on an iodide-induced Morita–Baylis–Hillman type reaction (a three-component assembly) followed by Suzuki–Miyaura cross-coupling are described.     

A convenient synthesis of 4(5)-(hetero)aryl-1H-imidazoles via microwave-assisted Suzuki–Miyaura cross-coupling reaction

A simple and rapid access to a variety of 4(5)-arylated imidazoles via palladium-catalyzed Suzuki–Miyaura cross-coupling reaction is described. Coupling parameters were screened for efficient C-4 arylation of N-unprotected 4-iodoimidazole with a broad range of boronic acids under microwave irradiation. Twenty-one imidazole derivatives were synthesized in modest to excellent yields in short reaction times.     

Pd–Co bimetallic nanoparticles supported on graphene as a highly active catalyst for Suzuki–Miyaura and Sonogashira cross-coupling reactions

Graphene (G) supported Pd–Co bimetallic nanoparticles (NPs) as a highly active catalyst was prepared by a chemical reduction method and used for coupling reactions. With the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectrum, the composition of resulting Pd–Co material was identified to be alloy structural. The Pd–Co (1:1)/G exhibited the highest catalytic activity for the Sonogashira-type coupling reactions and also exerted satisfied catalytic activity and recycle stability for Suzuki–Miyaura cross-coupling reactions. This Pd–Co/G material also possessed other advantages such as low-cost, easy recycled from reaction system by a magnet for their magnetic property, and easy experimental handling.     

Chemoselective Suzuki–Miyaura cross-coupling reactions of methyl 4-bromo-3-(trifluoromethylsulfonyloxy)-2-naphthoate

Arylated naphthalenes were prepared by Suzuki–Miyaura cross-coupling reactions of methyl 4-bromo-3-(trifluoromethylsulfonyloxy)-2-naphthoate. The reactions proceeded with very good chemoselectivity in favor of the triflate group, due to additive electronic ortho electronic effects.     

A simple and efficient tetradentate Schiff base derived palladium complex for Suzuki–Miyaura reaction in water

A simple and efficient catalytic system based on Pd complex of tetradentate Schiff base ligands is found to be highly active (up to 99% isolated yield) for Suzuki–Miyaura reaction of aryl bromides with arylboronic acids in water at room temperature. Further the scope of this protocol has been extended to the Suzuki–Miyaura cross-coupling reaction of aryl chlorides with arylbronic acids in isopropanol.     

Preparation of C-arylglycals via Suzuki–Miyaura cross-coupling of dihydropyranylphosphates

The preparation of C-arylglycals has been accomplished by employing the Suzuki–Miyaura cross-coupling reaction of dihydropyranylphosphates with arylboronate esters. The reaction is tolerant of both electron-donating (EDG) and electron-withdrawing (EWG) groups on the aromatic ring and affords the corresponding C-arylglycals in good to excellent yields (68–97%). Additionally, the ketene acetal phosphate derived from 6-deoxy-3,4-di-O-benzyl-l-rhamnal also couples efficiently to yield C-arylglycals in excellent yields.     

O-Aryloxime ether analogues as novel and efficient ligands for palladium-catalyzed Suzuki–Miyaura coupling in water

O-Aryloxime ether analogues L1–L3 were studied as ligands in palladium-catalyzed Suzuki–Miyaura cross-coupling reaction of aryl bromides and aryl boronic acids in water at room temperature. Reaction conditions for the cross-coupling were optimized using PdCl₂ and Pd(OAc)₂ under aerobic condition. From the three electronically diverse O-aryloxime ether ligands studied herein, the use of 1-phenyl-ethanone O-(4-chloro-phenyl)-oximeL2 exhibits the best catalytic system in the presence of K₂CO₃ as the base and TBAB as the promoter.     

Efficient synthesis of diversely substituted pyrimidines by palladium catalyzed Suzuki–Miyaura coupling

An efficient synthesis of 2-aryl/heteroaryl substituted pyrimidinyl ethanones 4(a–t) was developed using a palladium-catalyzed Suzuki–Miyaura coupling reaction strategy. Use of Pd(OAc)₂ in the presence of PPh₃ and Na₂CO₃ in 1,4-dioxane solvent was found to be the most effective reaction condition.     

Stereoselective total synthesis of ieodomycin C

A concise stereoselective synthesis of the marine natural product ieodomycin C (3) has been achieved from commercially available pyridinium-1-sulfonate (8) in eight linear steps and 14% overall yield. The key synthetic steps included a B-alkyl Suzuki–Miyaura cross-coupling reaction and an Evans–Nagao acetate aldol reaction. The same synthetic sequence was used for preparing the enantiomer of ieodomycin C (3). Our efforts confirmed the structure of the antibacterial natural product 3.     

Inhibition of (dppf)nickel-catalysed Suzuki–Miyaura cross-coupling reactions by α-halo-N-heterocycles

A nickel/dppf catalyst system was found to successfully achieve the Suzuki–Miyaura cross-coupling reactions of 3- and 4-chloropyridine and of 6-chloroquinoline but not of 2-chloropyridine or of other α-halo-N-heterocycles. Further investigations revealed that chloropyridines undergo rapid oxidative addition to [Ni(COD)(dppf)] but that α-halo-N-heterocycles lead to the formation of stable dimeric nickel species that are catalytically inactive in Suzuki–Miyaura cross-coupling reactions. However, the corresponding Kumada–Tamao–Corriu reactions all proceed readily, which is attributed to more rapid transmetalation of Grignard reagents.

Nickel complexes with a dppf ligand can form inactive dinickel(ii) complexes during Suzuki–Miyaura cross-coupling reactions. However, these complexes can react with Grignard reagents in Kumada–Tamao–Corriu cross-coupling reactions.     

Synthesis of highly soluble fluorescent π-extended 2-(2-thienyl)benzothiazole derivatives via oxidative cyclization of 2-thienylthioanilide as the key step

In this Letter, we synthesize highly soluble push–pull type fluorescent 2-(2-thienyl)benzothiazole dyes and evaluate their photophysical properties. The key step is the synthesis of 2-(5′-bromothien-2′-yl)-6-alkoxybenzothiazole (2) via oxidative cyclization of 2-thienylthioanilide using PhI(OAc)₂ as the oxidant. The target dyes could be easily synthesized by the Suzuki–Miyaura cross-coupling reaction of 2 and an appropriate π-donor. The photophysical properties of the 2-thienylbenzothiazole chromophore were controlled by the π-donor moiety. It was found that 2 exhibited large Stokes shifts (5345 cm⁻¹) and a high quantum efficiency for fluorescence (Φ_F = 0.94 in CH₂Cl₂). Therefore, it can be expected to be a useful photofunctional material in liquid crystal laser dyes and nonlinear optical materials.     

Efficient synthesis of neurotrophic honokiol using Suzuki–Miyaura reactions

Efficient synthesis of honokiol (1) was accomplished using two kinds of Suzuki–Miyaura reactions. The first Suzuki–Miyaura reaction was employed to couple 2-bromophenol (6) with 4-hydroxyphenylboronic acid (5), giving rise to biphenol 4, and the second coupling was used to introduce allyl groups at 5- and 3′-positions of honokiol. The total synthesis of 1 was completed in 74% yield over five steps from 6, or in 83% yield over four steps from biphenol 4.     

Exploration of versatile reactions on 2-chloro-3-nitroimidazo[1,2-a]pyridine: expanding structural diversity of C2- and C3-functionalized imidazo[1,2-a]pyridines

Alternative strategies for functionalizing 2-chloro-3-nitroimidazo[1,2-a]pyridine have been developed. Suzuki–Miyaura cross-coupling reaction provided easily the corresponding 2-arylated compounds, and herefrom the nitro group was reduced into amine which afforded amides, anilines, and ureas in the 3-position. The amination of the key compound using a metal-catalyzed reaction was reported. This study highlighted the importance of the nitro group to facilitate the chlorine displacement. Other nucleophilic aromatic substitutions open a route to various products derived from imidazo[1,2-a]pyridine.