Chiral palladacycle promoted asymmetric synthesis of functionalized bis-phosphine monoxide ligand

Zhang, Yi; Ding, Yi; Pullarkat, Sumod A.; Li, Yongxin; Leung, Pak‐Hing

doi:10.1016/j.jorganchem.2010.09.057

Cited by 8 publications

(5 citation statements)

References 28 publications

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“…The ability of alkynyl(dibenzo[ a , d ]cycloheptatrienol)Co 2 (CO) 6 complexes, such as 1b , to lose a carbonyl ligand, even at ambient temperature, and distort the seven‐membered ring so as to allow the C10=C11 double bond to bind at the vacant coordination site has already been discussed , . Apart from its relevance to the mechanism of the PKR, this also raises the possibility that the 5‐alkynyl‐5 H ‐dibenzo[ a , d ]cyclohepten‐5‐ol unit could function as a hemilabile ligand by reversible decoordination of the alkene moiety, thus allowing temporary access to a vacant site, analogous to the behaviour of numerous bisphosphine monoxide complexes …”

Section: Resultsmentioning

confidence: 99%

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

et al. 2017

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Under very mild conditions, (5-alkynyl-5H-dibenzo-[a,d]cycloheptatrien-5-ol)Co 2 (CO) 6 clusters 1 lose a carbon monoxide ligand and form the corresponding η 2 -alkene-μ-alkyne-Co 2 (CO) 5 complexes 2 (the first isolated examples of the initial phase of the Pauson-Khand reaction). This behaviour is not paralleled by the homologue in which an additional methylene group has been inserted within the seven-membered ring, as in the [5-alkynyl-6H-dibenzo[a,e]cyclooctatrienol]Co 2 -(CO) 6 system 8, for which several X-ray crystal structures are reported. The apparent additional flexibility of this molecular framework does not translate into conformations appropriate for the formation of η 2 -alkene-μ-alkyne-Co 2 (CO) 5 complexes. The relative inertness of the ethynyl complex 1a, compared [a] 2051 ing of the seven-membered ring towards the cluster, such that this distance, d, shortens to 2.04 Å. In contrast, in the eightmembered ring complex 8a, not only is the corresponding bond-centroid-to-cobalt distance, d, considerably longer (ca. 4.2 Å), but the C11=C12 double bond is also twisted away from the horizontal, as depicted in Figure 6b.

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Section: Resultsmentioning

confidence: 99%

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

et al. 2017

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“…As early as 1983 White et al established the structure of o -[C 6 H 4 (PMePh)(P(O)MePh)] bound to Ru; several other metals have since been observed in mixed bidentate P/PO complexes (for example Hg, Mo, Cu, Pt and Os) . However, limited examples of Pd complexation with bis-phosphine mono-oxides have been reported …”

Section: Resultsmentioning

confidence: 99%

Mono-Oxidation of Bidentate Bis-phosphines in Catalyst Activation: Kinetic and Mechanistic Studies of a Pd/Xantphos-Catalyzed C–H Functionalization

et al. 2015

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Kinetic, spectroscopic, crystallographic, and computational studies probing a Pd-catalyzed C-H arylation reaction reveal that mono-oxidation of the bis-phosphine ligand is critical for the formation of the active catalyst. The bis-phosphine mono-oxide is shown to be a hemilabile, bidentate ligand for palladium. Isolation of the oxidative addition adduct, with structural elucidation by X-ray analysis, showed that the mono-oxide was catalytically competent, giving the same reaction rate in the productive reaction as the Pd(II)/xantphos precursor. A dual role for the carboxylate base in both catalyst activation and reaction turnover was demonstrated, along with the inhibiting effect of excess phosphine ligand. The generality of the role of phosphine mono-oxide complexes in Pd-catalyzed coupling processes is discussed.

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“…We hypothesized that if the ligand were responsible for the observed attenuation, this could result from the phosphine acting as a sacrificial reductant. Xantphos oxides formed throughout catalysis could contribute to the epimerization attenuation via consumption of oxidants/base that could promote epimerization. − Xantphos oxide was indeed detected by HPLC-MS, , however, tracking the C–N coupling reaction beyond complete conversion showed that significant epimerization of product (3 S ,6 R )- 3 to (3 S ,6 S )- 3 only began upon the depletion of the observed [Pd] resting state, [Xantphos–Pd–Ar] + (Figure ). This relationship strongly suggested that the suppression of sultam C6 epimerization was related to the presence of a Pd(II) oxidative addition complex.…”

Section: Resultsmentioning

confidence: 99%

Investigating the Origin of Epimerization Attenuation during Pd-Catalyzed Cross-Coupling Reactions

Cai,

Malig,

Kurita

et al. 2024

ACS Catal.

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Palladium-catalyzed cross-couplings remain among the most robust methodologies to form carbon−carbon and carbon-heteroatom bonds. In particular, carbon−nitrogen (C−N) couplings (Buchwald− Hartwig aminations) find widespread use in fine chemicals industries. The use of base in these reactions is critical for catalyst activation and proton sequestration. Base selection also plays an important role in process design, as strongly basic conditions can impact sensitive stereocenters and result in erosion of stereochemical purity. Herein we investigate the role of a Pd catalyst in suppressing base-mediated epimerization of a sultam stereocenter during a C−N cross-coupling reaction to access the RORγ inhibitor GDC-0022. Online high-performance liquid chromatography-mass spectrometry (HPLC-MS) was employed to acquire reaction time course profiles and to delineate epimerization behavior, identify decomposition pathways, and monitor Pd-containing species. Our ability to monitor organopalladium complexes in real time by HPLC-MS provided strong evidence that the degree of epimerization was correlated to the Pd speciation in solution. Specifically, Pd(II) complexes were associated with mitigating epimerization of six-membered sultams. Additional studies showed that the suppression of epimerization in the presence of Pd(II) can impact Pd-catalyzed reactions of other substrates such as enolizable ketones, thus providing practical insight on the execution and optimization of such processes.

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Chiral palladacycle promoted asymmetric synthesis of functionalized bis-phosphine monoxide ligand

Cited by 8 publications

References 28 publications

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization

Mono-Oxidation of Bidentate Bis-phosphines in Catalyst Activation: Kinetic and Mechanistic Studies of a Pd/Xantphos-Catalyzed C–H Functionalization

Investigating the Origin of Epimerization Attenuation during Pd-Catalyzed Cross-Coupling Reactions

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