Domino Approach to Benzofurans by the Sequential Sonogashira/Hydroalkoxylation Couplings Catalyzed by New N-Heterocyclic-Carbene-Palladium Complexes

Zanardi, Alessandro; Mata, José A.; Peris, Eduardo

doi:10.1021/om900358r

Cited by 118 publications

(52 citation statements)

References 31 publications

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“…Based on ortho-iodo phenol or an ortho-iodo benzylalcohol as an aryl halide and phenylacetylene as an alkynyl coupling partner, a Pd-catalyzed domino sequence has been reported where cycloisomerization subsequent to the coupling step affords benzofuran 1 or benzoisofuran 2, respectively [44]. Three different NHC-Pd-pyridine complexes 3-5, where NHC is 1,2,4-trimethyltriazolyldiylidene (3), 1,3-dimethylimidazolylidene (4), and 1,4-dimethyltriazolylidene (5), respectively, have been successfully employed (Scheme 1).…”

Section: Sequences Based Upon Alkynylation and Carbopalladative Insermentioning

confidence: 99%

Sequentially Palladium-Catalyzed Processes in One-Pot Syntheses of Heterocycles

Lessing

Müller

2015

Applied Sciences

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Sequentially Pd-catalyzed processes are excellent entries to heterocycle synthesis. The broad mechanistic variety combined with often very mild reaction conditions allow the concatenation of elementary organic and organometallic steps to novel sequences in the sense of one-pot domino and multicomponent reactions. Given the numerous opportunities of alkyne coordination and their Pd-mediated transformations, alkynylation and carbometallation play a key role, both for purely organometallic sequences as well as in those processes that are intercepted by cyclocondensation. Pd-catalyzed aminations also find more and more entry into novel heterocycle syntheses based upon this theme.

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Section: Sequences Based Upon Alkynylation and Carbopalladative Insermentioning

confidence: 99%

Sequentially Palladium-Catalyzed Processes in One-Pot Syntheses of Heterocycles

Lessing

Müller

2015

Applied Sciences

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“…Complexes 230232 have been employed in a sequential Sonogashirahydroalkoxylation coupling for the synthesis of benzofurans, being 231 the most active catalyst. 82 Thus, 2-halophenylmethanols reacted with phenylacetylene in the presence of a complex (230232: 1 mol % of palladium) providing the expected (Z)-1-benzylidene-1,3-dihydroisobenzofuran (Table 6). Similarly, the reaction of 2-iodophenol with phenylacetylene formed the 2-phenylbenzofuran under the same reaction conditions.…”

Section: ç Sonogashira Reactionmentioning

confidence: 99%

Heterocyclic Carbene–Metal-catalyzed Csp2–Csp2 and Csp–Csp2 Couplings Using Nonmetallic Substrates

Yus¹,

Pastor²

2013

Chemistry Letters

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The use of carbene ligands for transition-metal complexes has been developed in the last decades, being of special interest those carbenes derived from a nitrogen-containing heterocyclic system. An interesting variety of carbenemetal complexes has been tested in the MizorokiHeck reaction. In comparison, few examples can be found for the MatsudaHeck version of this coupling reaction. Additionally, the Sonogashira coupling has been also catalyzed with different carbenemetal catalysts. Ç IntroductionN-Heterocyclic carbenes (NHCs) have emerged in the last years as a new family of ligands with interesting electronic and structural properties.1 The combination of their strong ·-donor and poor ³-acceptor abilities results in good coordination stability and versatility. Consequently, the use of NHC ligands based on imidazolium ions and related heterocycles has appeared as an alternative to phosphanes in the design of new organometallic catalysts.2 One of the main advantages of employing NHC-based catalysts compared with phosphanebased ones is that they are far less prone to oxidation, allowing their prolonged use, and reuse. Although NHCs were presented as simple tertiary phophane mimics, they have been recognized as much more over the past decade. Therefore, NHC ligands have become an interesting alternative to other types of ligands in different cross-coupling catalytic reactions mediated by transition metals.3 Moreover, the easy introduction of chiral elements in the corresponding precursors have made chiral NHCs promising chiral ligands in metal-based asymmetric catalysis. 4 The comparison between phosphane and NHC ligands, from a mechanistic point of view, has been studied, clear differences being found.5 First, the possibility of carbene ligand dissociation is greatly reduced due to its stronger donor ability; and second, the reactivity of the NHCmetal complex is higher probably caused by the lack of back-donation from the metal to the carbene ligand. Jutand and co-workers studied the reactivity of monocarbene and bis(carbene) Pd(0) complexes toward the oxidative addition of aryl halides, concluding that the electronic and steric properties of the carbene ligand are important factors in this step of the catalytic process. 6 Among the carboncarbon coupling reactions, the activation of a CH from an alkene (MizorokiHeck reaction) or an alkyne (Sonogashira reaction) are of special interest. This highlight review describes the progress on the topic of NHC ligands for transition-metal-catalyzed coupling reactions, employing nonmetallic reagents. Thus, both different NHC precursors and NHCmetal complexes with catalytic activity in the Mizoroki Heck, MatsudaHeck, and Sonogashira reactions are compiled. Ç Mizoroki-Heck ReactionIn 1995, Herrmann and co-workers introduced the use of bis(NHC)Pd complexes as catalysts with long-term stability in the MizorokiHeck reaction.7 Indeed, the carbenes derived from imidazole stabilized the palladium complexes due to their pronounced donor properties, being more stable toward...

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“…104 The reaction of 1,2,4-trimethyltriazolium bis(tetrafluoroborate) with palladium salts in coordinating solvents avoided polymeric structures and led to homobimetallic palladium complexes 39 and 40 (Scheme 14). 113,114 A slight modification in the reaction conditions using Pd(acac) 2 and Cs 2 CO 3 afforded the trimetallic palladacycle 41. 113 In this complex two of the palladiums are connected through the triazolyldiylidene ligand; the third metal center arises from a double C-H activation of the terminal methyl groups of two acac ligands.…”

Section: Scheme 14mentioning

confidence: 99%

“…114 The carbon-carbon bond formation worked without the need of additives other than the base. The cyclization process was highly selective towards the Z isomer and five member ring.…”

Section: Scheme 15mentioning

confidence: 99%