Synthesis of tetraaryl-p-benzoquinones by Suzuki-Miyaura cross-coupling reactions of tetrabromo-p-benzoquinone

Suzuki-Miyaura cross-coupling reactions of tetrabromo-p-benzoquinone provide a convenient approach to tetraaryl-p-benzoquinones.     

Synthesis of biphenylamines via Suzuki-Miyaura cross-coupling reactions

A small library of meta- and para-biphenylamines substituted by various alkyl, alkoxy, phenoxy, or halogeno groups on their aromatic rings was synthesized via Suzuki-Miyaura cross-coupling between bromoanilines and arylboronic acids using palladium catalysts. The experimental conditions were carefully adjusted to accommodate a wide range of substituents, in terms of electron-withdrawing or -donating ability and steric bulk. In some cases, protection and deprotection of the amine function via its trifluoroacetamide were added to the reaction sequence in order to facilitate the cross-coupling step.     

Synthesis of arylated chalcone derivatives via palladium cross-coupling reactions

A useful protocol for arylation of the olefin double bond of chalcones to afford tri- and tetra-substituted chalcone derivatives is reported. The protocol begins with the Heck reaction between chalcones and aryl iodides providing β-arylchalcones. This reaction tolerates various functional groups on both rings, as well as deactivated aryl iodides. The products are obtained in moderate to excellent yields and the (E)-β-arylchalcones (E:Z?>?96:4) can be isolated via precipitation. Competitive Heck reactions pointed to a significant effect of ring one substituents on the reaction rate, while substituents on ring two have a much smaller effect. To access α,β-diarylchalcones, a sequential bromination-Suzuki cross coupling strategy was applied to the β-arylated compounds which afforded double arylated chalcone derivatives in 60–99% yield over two steps.     

Synthesis of non-symmetrical alkynylpyridines by chemoselective Sonogashira cross-coupling reactions

4-Bromo-2,3,5-trichloro-6-iodopyridine was studied as a new substrate in chemoselective Sonogashira reactions. This approach provides an efficient access to non-symmetrical mono-, di-, tri- and pentaalkynylated pyridines in good yields. Selected pentaalkynylated pyridines were studied with regard to their UV/Vis- and emission properties showing moderate to high fluorescence quantum yields.     

Synthesis of 16-E-([aryl]idene)-3-methoxy-estrones by a palladium catalysed Mizoroki-Heck reaction

16-E-Arylidene-3-methoxy-estrones were synthesized using a palladium catalysed Mizoroki-Heck reaction. This methodology tolerates various functional groups and gives the corresponding products in yields between 14 and 99%, which were strongly dependent on the electronic character of the aryl halides.     

Synthesis of 2,3-disubstituted pyrazines and quinoxalines by Heck cross-coupling reactions of 2,3-dichloropyrazine and 2,3-dichloroquinoxaline. Influence of the temperature on the product distribution

Heck cross-coupling reactions of 2,3-dichloropyrazine provide a convenient approach to 2,3-dialkenyl-, 2-alkenyl-3-alkyl-, and 2,3-dialkylpyrazines depending on the reaction conditions.     

Polymer-supported palladium catalysed Suzuki-Miyaura reactions in batch and a mini-continuous flow reactor system

A polymer-supported palladium(II) salen-type complex exhibited catalytic activity in the cross-coupling reaction of various aryl bromides and heteroaryl bromides with phenylboronic acid in a mini-continuous flow reactor system at elevated temperatures in a phosphine-free system. The reaction was also performed in batch using a number of different solvent systems in order to optimise conditions. The catalytic mini-reactor can be used repeatedly over several cycles in the Suzuki-Miyaura cross-coupling reaction. While the diameter of the flow channel is 3 mm, the macroporous resin supported catalyst is solvent expanded to completely fill the channel. Consequently, the liquid path is through the micro channels of the macroporous resin structure. Intensification of the process over the stirred batch reaction is through increased reagent-catalyst contact and results in a 20-fold increase in the rate of reaction. The residence/space time on the reactor is 10.5 min, compared to 24 h in batch, which means that a diversity of starting materials can be screened over a short period of time. To demonstrate the utility of the system, a diversity of aryl and heteroaryl bromides have been studied.     

Synthesis of fluorenones based on a ‘[3+3] cyclization/Suzuki cross-coupling/Friedel-Crafts acylation’ strategy

Functionalized fluorenones were prepared by sequential ‘[3+3] cyclization-Suzuki cross-coupling/Friedel-Crafts acylation’ reactions.     

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.     

Unusual ligand-dependent chemoselective Suzuki-Miyaura cross-coupling reactions of 3-bromo-4-trifloyl-thiophenes

An unusual ligand-dependent chemoselective Suzuki-Miyaura cross-coupling reaction for 3-bromo-4-trifloyl-thiophenes was discovered. Pd(PPh₃)₄ showed selectivity for triflate over bromide, whereas the selectivity was reversed for Pd(^tBu₃P)₂.     

Highly selective mono-substitution in Pd-catalyzed cross-coupling reactions of 3,6-dichloropyridazine with organozinc compounds

Pd-catalyzed cross-coupling reactions of 3,6-dichloropyridazine (1) with benzyl, aryl, and alkyl organozinc compounds led to selective mono-substitution of one of the chlorine atoms. The subsequent cross-coupling of the resulting monochlorides with RZnCl afforded unsymmetrical 3,6-carbon-disubstituted pyridazines.     

Site-selective Suzuki-Miyaura reactions of 2,3,5-tribromo-N-methylpyrrole

The first Suzuki-Miyaura reactions of 2,3,5-tribromo-N-methylpyrrole are reported. These reactions proceed with very good site-selectivity in favour of position 5 which is more reactive than position 2, due to steric reasons. The second attack occurs at position 2 which is more electron deficient than position 3.     

Synthesis of conjugated enediynes via palladium catalyzed cross-coupling reactions of potassium alkynyltrifluoroborates

An efficient synthesis of cross-conjugated enediynes has been developed utilizing the palladium catalyzed cross-coupling reactions of 1,1-dibromo-1-alkenes with potassium alkynyltrifluoroborates under mild conditions.     

Expedient synthesis of 4-O-methylhonokiol via Suzuki-Miyaura cross-coupling

Concise and practical synthesis of 4-O-methylhonokiol was achieved in 34% overall yield. The key features of our synthesis include chemoselective ortho-mono bromination of phenol as well as biaryl formation via Suzuki-Miyaura cross-coupling, in which bromophenol was reacted with potassium aryltrifluoroborate using Pd(OAc)₂ and RuPhos under microwave conditions.     

Pd-CNT-catalyzed ligandless and additive-free heterogeneous Suzuki-Miyaura cross-coupling of arylbromides

Pd-CNT efficiently catalyzed Suzuki-Miyaura coupling of arylbromides under ligandless and additive-free conditions in aqueous media. For hydrophilic substrates, the reaction could be carried out in neat water.     

Two New Modes of Pd-Catalyzed Domino-Tetracyclization of Bromodienynes—5-exo-trig Cyclization Wins over β-Hydride Elimination

Remarkable increases of molecular complexity in a single procedural step are achieved with the title reaction. Only a slight modification in the substitution pattern on the acyclic precursor 2 can change the mode of tetracyclization to either yield skeletons of type 1 or 3 exclusively.     

5,6-Dihydropyrrolo[2,1-b]isoquinolines as scaffolds for synthesis of lamellarin analogues

Efficient modular synthetic routes to open chain marine alkaloids such as lamellarins have been developed. 5,6-Dihydropyrrolo[2,1-b]isoquinoline scaffolds were prepared, and protocols enabling regioselective bromination followed by Suzuki cross-coupling were established for the introduction of aryl groups onto the 2- and 3-positions.     

Esterification and Chemoselective Synthesis of R-Tetrahydrothiazo-2- thione-4-carboxylic Esters Catalyzed by TiCl4

A series of esters of R-tetrahydrothiazo-2-thione-4-carboxylic acid[R-TTCA] was synthesized by direct esterification of R-TTCA with alcohols(CH3OH,C2H5OH,n-C3H7OH,i-C3H7OH,n-C4H9OH,sec-C4H9OH)in the presence of TiCl4 as the catalyst at room temperature without using any other solvent or dehydrant in high yields,91.6%-99.1% for primary alcohols and 55%- 80% for secondary alcohols.The catalyst has a strong chemoselective activity for the esterification of primary alcohols with R-TTCA in the presence of secondary alcohols.Owing to high yield,high chemoselectivity,and mild conditions used,this is an efficient method for the esterification of primary alcohols with R-TTCA.     

Synthesis of macrocyclic precursors of lankacidins using Stille reactions of 4-(2-iodo-alkenyl)azetidinones and related compounds for ring closure

In the context of a proposed total synthesis of lankacidins, the synthesis of 4-(2-iodo-alkenyl)azetidinones and their participation in Stille coupling reactions have been investigated. 1-tert-Butyldimethylsilyl-4-(2-iodoethenyl)azetidinone was found to undergo a Stille coupling reaction with a 3-hydroxy-1-tributylstannylhepta-1,5-diene to give an acceptable yield of the corresponding conjugated diene but the analogous reaction with a 3-tert-butyldimethylsilyloxy-1-tributylstannylhepta-1,5-diene was unsuccessful. A series of 4-[(E)-2-iodoprop-1-enyl]azetidinones, a ring-opened ester and a lactone were also found to undergo Stille reactions with 3-tributylstannylprop-2-enol albeit with variable yields. Asymmetric syntheses of methyl (2R,3R,5S)-3-tert-butyldimethylsilyloxy-2-methyl-5-(2-trimethylsilylethoxy)methoxy-6-oxohexanoate, (3R,4S)-1-tert-butyldimethylsilyl-4-[(E)-2-iodoprop-1-enyl]-3-methylazetidin-2-one, and (5S,2E,6E)-5-tert-butyldimethylsilyloxy-2-methyl-1-phenylsulfonyl-7-tributylstannylhepta-2,6-diene and their incorporation into macrocyclic precursors of the lankacidins were then investigated. Key reactions were a Julia reaction between the aldehyde and the sulfone to form the 12,13-double-bond, a stereoselective acylation of the azetidinone, and formation of macrocycles using intramolecular Stille reactions in the presence of a free hydroxyl group at C(8) (lankacidin numbering).