Chiral sulfoxides and sulfides tethered to pyridines as ligands for enantioselective catalysis: Palladium catalyzed allylic substitution and addition of diethylzinc to benzaldehyde

Chelucci, Giorgio; Berta, Daniela; Saba, Antonio

doi:10.1016/s0040-4020(97)00113-0

Cited by 58 publications

(13 citation statements)

References 20 publications

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“…Stereoelectronically, the palladium−allyl terminus bond opposite the more powerful acceptor atom (phosphorus) will be longer and hence more susceptible to cleavage as a result of nucleophilic attack . Such physical attributes have been verified by NMR and X-ray studies and are claimed to control enantioselection. 8f, Heterobidentate nitrogen−sulfur ligands can also control the enantioselection of this process, − but many researchers rationalize results by analogy to nitrogen−phosphorus chelating systems. 10a,11d,13a, As part of an ongoing research program, we have developed a new series of heterodentate chelate ligands, derived from amino acids, where the chirality inherent to the backbone of the amino acid can be transmitted closer to the reaction center due to the correct choice of donor groups and substituents . The emphasis of this work is on understanding the origins of chirality induction in our ligand systems to aid the design of simpler, more efficient chiral ligands for asymmetric catalysis.…”

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confidence: 99%

Origins of Enantioselectivity with Nitrogen−Sulfur Chelate Ligands in Palladium-Catalyzed Allylic Substitution

et al. 1999

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The reaction of 1,3-diphenyl-2-propenyl acetate (9) with dimethylmalonate to give the substitution product 10 is effectively catalyzed by Pd complexes containing chiral imine-sulfide chelate ligands derived from amino acids. The ligand of choice, (S)-N-2'-chlorobenzylidene-2-amino-3-methyl-1-thiophenylbutane (6e), prepared in only two steps from (S)-valinol, gave an ee of 94%. Because the explanation of selectivity with the majority of other nitrogen-sulfur chelate ligands in this reaction assumes the selectivity to be controlled by an electronic bias, which contradicts our results, we characterized the Pd-allyl intermediate 14 by X-ray diffraction and solution NMR. The possible mechanism of chirality transfer is discussed. The site of nucleophilic attack on the allyl ligand is not trans to the perceived better pi-acceptor ligand (sulfur), which would be analogous to chiral nitrogen-phosphorus systems. This reaction occurs trans to the imine donor, and the enantioselectivity is ultimately controlled by the subtle steric environment of the chiral imine-sulfur chelate ligand, which predisposes the allyl unit of the reaction intermediate to a preferred reaction trajectory. In light of results that emphasize the power of electronic desymmetrization for chiral recognition, these results suggest that electronically dissimilar ligands may not give rise to chiral recognition through electronic dissimilarity.

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confidence: 99%

Origins of Enantioselectivity with Nitrogen−Sulfur Chelate Ligands in Palladium-Catalyzed Allylic Substitution

et al. 1999

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“…Use of ligand 22 , which is only chiral at the sulfur atom, provided adduct 19 in a diminished 49 % ee , demonstrating the importance of the oxazolidine chirality for the selectivity. Building on this report, Chelucci and co‐workers reported the ability of tethered pyridine‐sulfoxide ligands to catalyze the same reaction, even though the highest selectivity observed was 34 % ee 15…”

Section: Sn Ligandsmentioning

confidence: 82%

Development of Chiral Sulfoxide Ligands for Asymmetric Catalysis

2015

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Nitrogen-, phosphorus-, and oxygen-based ligands with chiral backbones have been the historic workhorses of asymmetric transition-metal-catalyzed reactions. On the contrary, sulfoxides containing chirality at the sulfur atom have mainly been used as chiral auxiliaries for diastereoselective reactions. Despite several distinct advantages over traditional ligand scaffolds, such as the proximity of the chiral information to the metal center and the ability to switch between S and O coordination, these compounds have only recently emerged as a versatile class of chiral ligands. In this Review, we detail the history of the development of chiral sulfoxide ligands for asymmetric catalysis. We also provide brief descriptions of metal-sulfoxide bonding and strategies for the synthesis of enantiopure sulfoxides. Finally, insights into the future development of this underutilized ligand class are discussed.

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“…37,38 In contrast to the great variety of ligands based on the pyridine framework, which have proven to give very good levels of enantioselectivity in the catalyzed asymmetric C-C bond forming reactions with allylic compounds, 10 rare examples of application in this reaction of sulphur-containing pyridine ligands have been reported. [40][41][42][43] In order to define the scope and limitations of thienylpyridines as chiral controllers for asymmetric catalysis, Chelucci et al have first examined these N-S ligands in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2enylacetate with dimethyl malonate, which serve as a model substrate and reagent to compare the outcome of different ligands(Figure 7). 36 Though the protocol using the malonate anion obtained by Trost's procedure is generally the best way to carry out allylic substitution reactions, the use of preformed sodium dimethyl malonate, generated by the use of sodium hydride in THF, may in some cases offer best results.…”

Section: Palladium-catalyzed Allylic Alkylationmentioning

confidence: 99%