Recyclable Hybrid Silica‐Based Catalysts Derived from Pd–NHC Complexes for Suzuki, Heck and Sonogashira Reactions
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Abstract Two silylated Pd–NHC complexes were immobilized on hybrid silicas by sol‐gel cocondensation with tetraethyl orthosilicate (TEOS) and performed well as recyclable catalysts towards the Heck, Suzuki, and Sonogashira coupling reactions. Remarkable conversion and recyclability were achieved in the Suzuki reaction with a challenging aryl chloride. No side products and no undesired homocoupling were observed in Suzuki or Heck reactions, which facilitates the final purification step for the cross‐coupling products. High turnover numbers and turnover frequencies were found for copper‐ and phosphane‐free Sonogashira reaction between p ‐bromoacetophenone and phenylacetylene.Keywords:
Sonogashira coupling
Heck Reaction
Phenylacetylene
Suzuki reaction
Turnover number
Preparation and characterization of the first examples of copper(I) ferrocenylpolyphosphine complexes are reported. The molecular structure of complex {P,P′,P′′-[1,1′,2,2′-tetrakis(diphenylphosphino)-4,4′-di-tert-butylferrocene]iodocopper(I)} (1) was solved by X-ray diffraction studies, and its fluxional behavior in solution was investigated by VT-31P NMR; both revealed a net triligated coordination preference of the ferrocenyl tetraphosphine Fc(P)4tBu with copper. The tetradentate ligand is an active auxiliary in Sonogashira alkynylation; therefore the general question of copper as a competitive coordination partner in the Pd/Cu-catalyzed Sonogashira reaction was raised and discussed. Electronically neutral, activated, and deactivated aryl bromides were employed for coupling with phenylacetylene with various [(Pd)/(Cu)/(tetraphosphine)] systems. The catalytic investigations shown that 1 mol % of complex 1 in combination with palladium is far more effective and selective for Sonogashira coupling than 5 mol % of CuI and palladium in the coupling to phenylacetylene of the deactivated aryl bromide 4-bromoanisole. This system efficiently avoids the concurrent and deleterious consumption of phenylacetylene by formation of diyne or enynes. To our knowledge, this is the first time that this kind of high selectivity is induced in Sonogashira alkynylation by initial ligand complexation to copper instead of palladium. These results demonstrate that coordination of Cu halide cocatalyst is a factor that should no longer be neglected in mechanistic and applied studies of the Sonogashira reaction.
Sonogashira coupling
Phenylacetylene
Coupling reaction
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Sonogashira coupling
Phenylacetylene
Coupling reaction
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Abstract A standard Sonogashira coupling protocol has been applied for the preparation of a C 3 ‐symmetric phenylacetylene ( 2 ) and the corresponding linear phenylacetylene ( 3 ) incorporating terminal biphenyl substituents. The study of the mesomorphic properties of the target compounds, as well as mixtures of both, reveals that only the calamitic biphenylylacetylene 3 forms smectic liquid crystals. Upon investigating the electronic situation of both biphenylylacetylenes by spectroscopic methods and computational calculations, it becomes evident that 2 can be considered the trimeric analogue of 3 which however does not form liquid crystalline phases.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Phenylacetylene
Sonogashira coupling
Biphenyl
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By a combination of kinetic and theoretical studies it is concluded that gold is intrinsically active to perform the Sonogashira coupling reaction between phenylacetylene and iodobenzene. The presence of Pd impurities is not mandatory for catalyst activity.
Phenylacetylene
Sonogashira coupling
Iodobenzene
Coupling reaction
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Sonogashira coupling of phenylacetylene with iodobenzene has been studied in the presence of metallic Rh nanoparticle catalysts and found to occur via a surface-mediated heterogeneous route. Homogeneous catalytic processes due to Rh species that may leach into solution were barely detectable within the sensitivity of our experiments. Moreover, larger (8 nm) nanoparticles were found to be much better catalysts than very small ones (2 nm), which is consistent with the hypothesis that steric limitations adversely affect the efficiency of the latter.
Phenylacetylene
Iodobenzene
Sonogashira coupling
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Phenylacetylene
Sonogashira coupling
Microemulsion
Alkyne
Coupling reaction
Reactivity
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Electrochemical oxidation of catechols (1a-1c) is studied in the presence of phenylacetylene (3) as a nucleophile in an ethanol-phosphate buffer (pH 7.5, 0.20 M) mixture (green media) by means of voltammetric methods. The results indicate that the o-quinones (2a-2c) are derived from 1a-1c participation in a Sonogashira-type coupling reaction, with phenylacetylene (3) to form the corresponding new benzoquinones (9a-9c). The electroorganic synthesis of these compounds (9a-9c) has been successfully performed in an undivided cell with good yield and purity.
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Phenylacetylene
Coupling reaction
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Abstract Several phenylacetylenes were coupled under Sonogashira cross‐coupling conditions with the methyl esters of N ‐( tert ‐butoxycarbonyl)‐( E )‐β‐bromo‐ or ‐β,β‐dibromodehydroalanine, to give β‐substituted or β,β‐disubstituted dehydroalanines, respectively. The β‐substituted dehydroalanines were obtained in good to high yields (60−90%) under the usual Sonogashira conditions (1 equiv. of the phenylacetylene, 1 mol % of [Pd(PPh 3 ) 4 ], 2 mol % of CuI, 18 equiv. of NEt 3 in acetonitrile, 24 h at room temp.), with retention of stereochemistry. The β,β‐disubstituted dehydroalanines were, in turn, obtained in moderate to good yields (44−63%) under modified Sonogashira conditions (4 equiv. of the phenylacetylene,10 mol % of [PdCl 2 (PPh 3 ) 2 ], 20 mol % of CuI, 1.4 equiv. of Cs 2 CO 3 in acetonitrile, 2 h at reflux). In the latter reactions, some phenylacetylene dimer and the ( E ) isomer of the monosubstituted coupled products were also isolated to some extent. The Sonogashira products obtained from the 4‐bromophenylacetylene were allowed to react with functionalized benzo[ b ]thiophenes under C−C or C−N palladium‐catalyzed cross‐coupling conditions. Preliminary fluorescence studies were performed for mono‐ and disubstituted (4‐aminophenyl)acetylenic dehydroamino acids and for the benzo[ b ]thiophene derivatives. The results showed that some of the dehydroalanines prepared can be used as fluorescent probes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Phenylacetylene
Sonogashira coupling
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Abstract 1,3-Disubstituted-5-chloro-4-iodopyrazoles are selectively coupled with phenylacetylene under typical Sonogashira reaction conditions [PdCl2(PPh3)2, CuI, Et3N, dimethylformamide (DMF)] to obtain the corresponding 5-chloro-4-(phenylethynyl)pyrazoles in good yield. The latter are smoothly cyclized with Na2S in DMF into the corresponding thieno[2,3-c]pyrazoles. Detailed spectroscopic investigations (1H, 13C, and 15N NMR, mass, and infrared) of all compounds are reported.
Phenylacetylene
Sonogashira coupling
Dimethyl formamide
Acetylene
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Abstract Synthetic efforts toward the preparation of rotaxane precursors based on phenylacetylene macrocycles (PAM) are described. The aim of this study was to determine the optimal structural parameters to prepare high‐molecular‐weight rotaxane precursors through a strategy involving two Sonogashira couplings to attach bulky blockers on the PAM core. PAMs with different sizes and functions were prepared and coupled to different blockers to assess whether or not the resulting structure adopts a rotaxane‐like conformation in which the rigid rod forms after the Sonogashira coupling threads through the PAM.
Phenylacetylene
Rotaxane
Sonogashira coupling
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