Iridium‐Catalyzed Enantioselective Pauson—Khand‐Type Reaction of 1,6‐Enynes.

Shibata, Takanori; Toshida, Natsuko; Yamasaki, Mitsunori; Maekawa, Shunsuke; Takagi, Kentaro

doi:10.1002/chin.200603058

Cited by 3 publications

(3 citation statements)

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“…159 The authors further improved the protocol by reducing the partial pressure of carbon monoxide. 160 Lu et al have accomplished a highly enantioselective (up to 97% ee) preparation of 230 by using cationic iridium complexes (S)-234 derived from chiral phosphine-oxazoline (S)-233 (Scheme 68). 161 The nature of the anion was found to have a significant influence on both the enantioselectivity and the yield.…”

Section: Pauson−khand Reactionsmentioning

confidence: 99%

Synthesis of Chiral Cyclopentenones

et al. 2016

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The cyclopentenone unit is a very powerful synthon for the synthesis of a variety of bioactive target molecules. This is due to the broad diversity of chemical modifications available for the enone structural motif. In particular, chiral cyclopentenones are important precursors in the asymmetric synthesis of target chiral molecules. This Review provides an overview of reported methods for enantioselective and asymmetric syntheses of cyclopentenones, including chemical and enzymatic resolution, asymmetric synthesis via Pauson-Khand reaction, Nazarov cyclization and organocatalyzed reactions, asymmetric functionalization of the existing cyclopentenone unit, and functionalization of chiral building blocks.

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Section: Pauson−khand Reactionsmentioning

confidence: 99%

Synthesis of Chiral Cyclopentenones

et al. 2016

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“…Iridium complexes play important roles in oxidation (e.g., of alcohols [4][5][6], phenols [7][8][9], and amines [10,11]), hydrogenation [12,13], C-H activation [14][15][16], cycloaddition (e.g., [2 + 2 + 2] [17][18][19], [2 + 2 + 1] [20,21], and [4 + 2] [22,23]), cycloisomerization [1,2], and ring-opening reactions [24]. The richness of this chemistry explains the broad interest in the properties of the family of iridium complexes and clusters [25].…”

Section: Introductionmentioning

confidence: 99%

Structures, relative energies, and ligand dissociation energies of iridium carbonyl phosphine clusters

Zhang

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Gates

et al. 2015

Computational and Theoretical Chemistry

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a b s t r a c tThere is significant interest in the catalytic properties of substituted iridium carbonyl clusters but little thermodynamic information available characterizing them. The low-energy isomers of Ir x (PH 3 ) y (CO) z (x = 1, 2, 4) were investigated with density functional theory and correlated molecular orbital theory at the coupled cluster CCSD(T) level. The relative energies and ligand dissociation energies were calculated. Differences in relative energies are consequences of both electronic and steric effects of the phosphines and carbonyls. The calculations predict three fundamental structural types for Ir 2 (PH 3 ) y (CO) z : C 2v , C 2 , and D 3d . Ten exchange-correlation functionals were used for the ligand dissociation energy calculations in addition to CCSD(T) for the smaller clusters. The xB97X-D functional gave the most consistent ligand dissociation energies as compared with the CCSD(T) benchmark calculations, and, so it was used to predict the dissociation energies for larger clusters when CCSD(T) calculations were infeasible. The dissociation energies characteristic of Ir 4 (PH 3 ) y (CO) z were in the range of $30 to $60 kcal/mol. Dissociation of a bridging ligand often involved a hydrogen atom transfer from a phosphine to a coordinatively unsaturated iridium atom and a phosphine converting from a bridging site to an equatorial site. The products of such reactions are predicted to have lower relative energies than other isomers.Phosphines act as r-electron donors, and there is a trend of an increase in carbonyl ligand dissociation energies as more phosphines are substituted in the small clusters.

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“…10 The catalytic activities of small iridium clusters extend to numerous reactions, 11 including oxidation, hydrogenation, C− H bond activation, cycloaddition, cycloisomerization, 12,13 and ring-opening. 14 Mononuclear iridium complexes have also been widely used as catalysts in oxidation (e.g., of alcohols, 15−17 phenols, 18−20 and amines 21,22 ), C−H bond activation, 23−25 hydrogenation, 26,27 cycloaddition (e.g., [2 + 2 + 2], 28−30 [2 + 2 + 1], 31,32 and [4 + 2] 33,34 ), cycloisomerization, 12,13 and ringopening reactions. 35 Ir(CO) n (n = 1−4) and Ir 2 (CO) 8 clusters have been reported to be the products of the reaction of Ir with CO. 36−38 Ir 2 (CO) 8 clusters generated in matrices at 10−50 K dimerized into Ir 4 (CO) 12 at ∼200 K. 36,37 Recently, we reported a theoretical investigation of iridium carbonyl phosphine complexes Ir x (PH 3 ) y (CO) z (x = 1, 2, 4) 39 after earlier work showed that the tetrairidium clusters could have more than one kind of active site, in which the reactivity at the apical Ir site was controlled by three calixarene-phosphine ligands bonded to the basal plane.…”

Section: ■ Introductionmentioning

confidence: 99%

Role of N-Heterocyclic Carbenes as Ligands in Iridium Carbonyl Clusters

et al. 2017

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The low-energy isomers of Ir(CO)(NHC) (x = 1, 2, 4) are investigated with density functional theory (DFT) and correlated molecular orbital theory at the coupled cluster CCSD(T) level. The structures, relative energies, ligand dissociation energies, and natural charges are calculated. The energies of tetrairidium cluster are predicted at the CAM-B3LYP level that best fit the CCSD(T) results compared with the other four functionals in the benchmark calculations. The NHC's behave as stronger σ donors compared with CO's and have higher ligand dissociation energies (LDEs). For smaller isomers, the increase in the LDEs of the CO's and the decrease in the LDEs of the NHC's as more NHC's are substituted for CO's are due to π-back-bonding and electron repulsion, whereas the trend of how the LDEs change for larger isomers is not obvious. We demonstrate a μ-CO resulting from the high electron density of the metal centers in these complexes, as the bridging CO's and the μ-CO's can carry more negative charge and stabilize the isomers. Comparison of calculations for a mixed tetrairidum cluster consisting of two calixarene-phosphine ligands and a single calixarene-NHC ligand in the basal plane demonstrated good agreement in terms of both the ligand substitution symmetry (C derived), as well as the infrared spectra. Similar comparisons were also performed between calculations and experiment for novel monosubstituted calixarene-NHC tetrairidium clusters.

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Iridium‐Catalyzed Enantioselective Pauson—Khand‐Type Reaction of 1,6‐Enynes.

Cited by 3 publications

References 1 publication

Synthesis of Chiral Cyclopentenones

Synthesis of Chiral Cyclopentenones

Structures, relative energies, and ligand dissociation energies of iridium carbonyl phosphine clusters

Role of N-Heterocyclic Carbenes as Ligands in Iridium Carbonyl Clusters

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