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.     

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.     

Palladium-catalyzed Suzuki cross-coupling reactions in a microemulsion

An enhancement of palladium-catalyzed Suzuki cross-coupling reactions between substrates possessing long-chain alkyl or oxyalkyl substituents in two-phase media, in the presence of sodium dodecylsulfate, is shown. Quantitative evaluations of the influence of SDS on the reaction rates were determined.     

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.     

Palladium catalyzed atom-efficient cross-coupling reactions of triarylbismuths with aryl bromides

Aryl bromides (3 equiv) were coupled efficiently with triarylbismuths (1 equiv) in an atom-efficient way using the Pd(OAc)₂/PPh₃ catalytic system in the presence of K₃PO₄ as base in DMF at 90 °C, providing excellent yields of the cross-coupled biaryls in short reaction times.     

Activity of palladium on charcoal catalysts in cross-coupling reactions

Comparison of the activity of several commercially available Pd/C catalysts in C-C, C-N, and C-S bond forming cross-coupling reactions has demonstrated the importance of the choice of the catalyst source. Investigations showed marked difference in activity between the catalysts. Moreover, the catalytic activity of each catalyst varies with respect to the coupling. The first Pd/C catalyzed Hiyama coupling is reported.     

A new palladium catalyzed protocol for atom-efficient cross-coupling reactions of triarylbismuths with aryl halides and triflates

A new palladium catalyzed protocol for an atom-efficient cross-coupling reaction of triarylbismuths with aryl halides and triflates has been described. The palladium catalytic system with Cs₂CO₃ base was found to be very efficient in DMA solvent to furnish excellent yields of cross-coupled functionalized biaryls in short reaction times.     

Suzuki cross-coupling reaction of fluorobenzene with heterogeneous palladium catalysts

In this work, we accomplished for the first time the Suzuki cross-coupling reaction between fluorobenzene and phenylboronic acid with different heterogeneous catalysts and bases. The conversion values obtained are similar to those provided by homogeneous catalysts and activated aryl fluorides.     

Impregnated palladium on magnetite, a new catalyst for the ligand-free cross-coupling Suzuki-Miyaura reaction

A new catalyst for the cross-coupling Suzuki-Miyaura reaction is reported. The impregnated palladium on magnetite catalyst is very easy to prepare using the standard impregnation methodology. This catalyst avoids the use of any type of expensive and difficult handle organic ligand, showing excellent yields, under mild reaction conditions, for the classical formation of biaryl compounds. The catalyst is very easy to remove from the reaction medium, only by using a simple magnet, and it could be re-used up to three times with only a slightly decrease of the chemical yield.     

Preparation of 2,2-difluoro-1-trialkylsilylethenylstannanes and their cross-coupling reactions

Reaction of 2 with bis(tributyltin) in the presence of 3 mol % Pd₂(dba)₃, 6 mol % XPhos, and 30 equiv of LiBr in wet and air bubbled THF at reflux for 8 h afforded the desired products 3 in 73–74% yields. The cross-coupling reaction of 3a with aryl iodides in the presence of 10 mol % Pd(PPh₃)₄ and 10 mol % CuI afforded the coupled products 4a–p in 47–90% yields. The coupling reaction of 3b with various alkynyl bromides having aryl-, alkyl, or trialkylsilyl group also afforded the corresponding 1,3-enynes 5a–g in 61–77% yields.     

Practical synthesis of 6-aryluridines via palladium(II) acetate catalyzed Suzuki-Miyaura cross-coupling reaction

Sugar-protected 6-halouridine derivatives underwent Suzuki-Miyaura cross-coupling reactions with arylboronic acids in the presence of palladium(II) acetate as a catalyst, triphenylphosphine as a ligand, and sodium carbonate as a base. This methodology is applicable to both the C5- and C6-position of uridine and provides a direct access for versatile uridine derivatives.     

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.     

Syntheses of 4-(1-alkynyl)-2(5H)-furanones and coumarins via the palladium catalyzed cross-coupling reactions of potassium alkynyltrifluoroborates

An efficient synthesis of 4-(1-alkynyl)-2(5H)-furanones has been developed utilizing a palladium catalyzed coupling reaction of β-tetronic acid bromide with potassium alkynyltrifluoroborates in the absence of base. 4-Alkynylcoumarins were also synthesized using this method. The reactions are straightforward and the yields are excellent.     

Cobalt-catalyzed sequential cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives with Grignard reagents and their application to the synthesis of 1,3-diols

Cobalt/N-heterocyclic carbene system or cobalt/diamine combination effectively catalyzes sequential cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives with trialkylsilylmethyl, 1-alkynyl, and aryl Grignard reagents. The sequential cyclization/cross-coupling reactions are applied to the synthesis of 1,3-diols starting from siloxy-tethered 6-halo-1-hexene derivatives.     

Suzuki reactions catalyzed by palladium complexes bearing the bulky (2,6-dimesitylphenyl)dimethylphosphine

A new bulky and stable phosphine (2,6-dimesitylphenyl)dimethylphosphine, and representative palladium complexes have been prepared and structurally characterized; some of these complexes prove efficient for coupling of aryl chlorides with arylboronic acids.     

Palladium-catalyzed direct cross-coupling reaction between indenes and electron-deficient alkenes

An efficient methodology for oxidative cross-coupling of indene and derivatives with electron-deficient olefins catalyzed by palladium was developed. The corresponding diene products were obtained in moderate to good yields.     

Preparation of 2,3-disubstituted indoles by sequential Larock heteroannulation and silicon-based cross-coupling reactions

A simple and convergent synthesis of 2,3-disubstituted indoles has been developed using a sequential Larock indole synthesis and silicon-based, cross-coupling reaction. Substituted 2-iodoanilines reacted with an alkynyldimethylsilyl tert-butyl ether to afford indole-2-silanols under the Larock heteroannulation conditions after hydrolysis. The corresponding sodium 2-indolylsilanolate salts successfully engaged in cross-coupling with aryl bromides and chlorides to afford multi-substituted indoles. The development of an alkynyldimethylsilyl tert-butyl ether as a masked silanol equivalent enabled a smooth heteroannulation process and the identification of a suitable catalyst/ligand combination provided for a facile cross-coupling reaction.     

Sequential ring-closing metathesis/Pd-catalyzed, Si-assisted cross-coupling reactions: general synthesis of highly substituted unsaturated alcohols and medium-sized rings containing a 1,3-cis-cis diene unit

A sequential ring-closing metathesis/silicon-assisted cross-coupling protocol has been developed. Alkenyldimethylsilyl ethers of allylic, homoallylic and bis(homoallylic) alcohols undergo facile ring closure with Schrock's catalyst to afford 5-, 6-, and 7-membered cycloalkenylsiloxanes, respectively, in some cases with substituents on both alkenyl carbons. These siloxanes are highly effective coupling partners that afford styrenes and dienes (with various aryl and alkenyl halides) in high yield and specificity as well as good functional group compatibility. The siloxanes bearing a Z-iodoalkenyl tether undergo an intramolecular coupling process in the presence of [allylPdCl]₂ which constitutes a powerful method for the construction of medium-sized rings with an internal 1,3-cis-cis diene unit. The formation of 9-, 10-, 11-, and 12-membered carbocyclic dienes is achieved in good yield. Extension to the synthesis of 9-membered ring unsaturated ethers has also been accomplished. Noteworthy features of this process include: (1) highly stereospecific intramolecular coupling, (2) flexible positioning of the revealed hydroxy group, and (3) potential extension to other medium-sized carbocycles and heterocycles.     

Vinyl nosylates as partner in copper and silver co-catalyzed Sonogashira cross-coupling reactions

Vinyl nosylates, readily obtained from β-dicarbonyl derivatives, could be efficiently engaged in Sonogashira cross-coupling reactions, either cocatalyzed by copper or silver salts. The para-nitrobenzenesulfonate (nosylate) group allows this coupling to be performed under very mild conditions (room temperature). These new leaving group and mild conditions could be applied to the synthesis of acetylenic coumarinyl derivatives and to the total synthesis of an acetylenic monoterpene natural product, named cleviolide.     

Highly efficient synthesis of 1,2-disubstituted acetylenes derivatives from the cross-coupling reactions of 1-bromoalkynes with organoalane reagents

A Highly efficient route for the synthesis of 1,2-disubstituted acetylene derivatives has been developed by palladium catalyzed cross-couplings of alkynyl halides with (hetero)aryl aluminium reagents under mild conditions. This has given corresponding cross-coupling products good to excellent isolated yields of up to 99%. The aryls bearing electron-donating or electron-withdrawing groups in either alkynylhalides or arylaluminum substrates gave cross-coupling products good yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 1,2-disubstituted acetylenes derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.