Probing Electronic Effects in the Asymmetric Heck Reaction with the BIPI Ligands

Busacca, Carl A.; Grossbach, Danja; So, Regina C.; O’Brien, Erin M.; Spinelli, Earl

doi:10.1021/ol0340179

Cited by 146 publications

(46 citation statements)

References 11 publications

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“…It was found that O-ethyl 2-fl uorobenzimidate tetrafl uoroborate salt 11, a reagent introduced recently by Busacca et al for the synthesis of phosphinoimidazoline ligands, 26 provides an excellent nucleus for the assembly of a focused array of PHOX ligands. The approach taken is illustrated in Scheme 1, and involves initial condensation of a chiral amino alcohol with 11, followed by introduction of the desired diarylphosphino group by nucleophilic aromatic substitution upon the resulting (2-fl uoro)aryloxazoline.…”

Section: Resultsmentioning

confidence: 99%

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

Berkowitz

Shen

Maiti

2004

Tetrahedron: Asymmetry

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Section: Resultsmentioning

confidence: 99%

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

Berkowitz

Shen

Maiti

2004

Tetrahedron: Asymmetry

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“…[4] However, they have never been used in Pd-catalyzed asymmetric allylic substitution reactions, a domain where PHOX ligands are one of the most important players. [1d,5] We wish to report in the present paper the structural optimization of modular PHIM ligands using the Pd-catalyzed asymmetric allylic substitution reaction as a benchmark.…”

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confidence: 99%

“…Thus, ligands 11 and 12 were prepared through CuAAC reactions [9] from N-propargylic derivatives 13 and 14 (Scheme 1). The triazole moieties were installed by reaction with benzyl bromide in the presence of sodium azide, l-ascorbic acid and catalytic amounts of CuSO 4 , and the phosphino units were introduced in [b] By NMR. [c] By HPLC on a chiral stationary phase.…”

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Changing the Palladium Coordination to Phosphinoimidazolines with a Remote Triazole Substituent

et al. 2011

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Phosphinoimidazoline (PHIM) ligands bearing a triazolylmethyl substituent at the sp 3 nitrogen atom in the imidazoline ring lead to highly improved enantioselectivity (up to 99% ee) in allylic substitution reactions with respect to analogous ligands with substituents lacking the triazole unit. NMR and theoretical studies support a shift in the coordination mode of the PHIM ligand to palladium, triggered by a very favourable interaction with the triazole unit.Keywords: allylic substitution; asymmetric catalysis; palladium; phosphinoimidazoline ligands; triazole ligands Phosphinooxazolines (PHOX) [1] are versatile C 1 -symmetric chiral ligands (Figure 1, left) with ample applications in a variety of metal-catalyzed reactions. The analogous phosphinoimidazoline (PHIM) ligands (Figure 1, right) could represent an even more convenient alternative: the topology of the imidazoline ligand allows the use of readily available C 2 -symmetric diamine fragments, while the second nitrogen atom represents an additional source of molecular diversity (R 2 ), allowing the programmed modification of the electronic properties of the coordinating nitrogen atom. The additional nitrogen atom could also serve for the heterogenization of the phosphinoimidazoline ligand onto insoluble organic resins, a field which still remains completely unexplored.PHIM ligands have shown to be very efficient in the Ir-catalyzed enantioselective hydrogenation of prochiral olefins [2] and imines, [3] as well as in the Pdcatalyzed asymmetric Heck reaction.[4] However, they have never been used in Pd-catalyzed asymmetric allylic substitution reactions, a domain where PHOX ligands are one of the most important players. [1d,5] We wish to report in the present paper the structural optimization of modular PHIM ligands using the Pd-catalyzed asymmetric allylic substitution reaction as a benchmark. A first generation of PHIM ligands results from the optimization of the substituents at C-4 and C-5 on the imidazoline moiety (R 1 ), the substituent at the non-coordinating nitrogen atom of the imidazoline ring (R 2 ), and the substituents of the phos-

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“…Among the many PHOX analogues that we tested, readily available phosphinites of type 12 and 13 proved to be the most versatile ligands. Subsequently, we added phosphinoimidazolines, such as type 14, to our collection of ligands (32,33), as well as pyridine-and quinoline-derived P,N-ligands of type 15 and 16 (34), all of which gave very promising results. Recently, other research groups have become interested in this class of catalysts and have reported additional variants of Ir complexes with P,N-ligands (35)(36)(37)(38)(39)(40) and, as a further modification, oxazoline ligands with a heterocyclic carbene unit instead of a phosphino group (41).…”

Section: Figmentioning

confidence: 99%

Design of Chiral Ligands for Asymmetric Catalysis: From C₂‐Symmetric P,P‐ and N,N‐Ligands to Sterically and Electronically Nonsymmetrical P,N‐Ligands

Pfaltz

Drury

2004

ChemInform

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For a long time, C2-symmetric ligands have dominated in asymmetric catalysis. More recently, nonsymmetrical modular P,N-ligands have been introduced. These ligands have been applied successfully in various metal-catalyzed reactions and, in many cases, have outperformed P,P-or N,N-ligands.M ost asymmetric catalysts that have been developed so far are metal complexes with chiral organic ligands. The chiral ligand modifies the reactivity and selectivity of the metal center in such a way that one of two possible enantiomeric products is formed preferentially. Based on this concept, many metal complexes have been found that catalyze various reactions with impressive enantioselectivity. Despite impressive progress in this field, the design of suitable chiral ligands for a particular application remains a formidable task. The complexity of most catalytic processes precludes a purely rational approach based on mechanistic and structural criteria. Therefore, most new chiral catalysts are still found empirically, with chance, intuition, and systematic screening all playing important roles. Nevertheless, for certain reactions such as Rh-catalyzed hydrogenation (1, 2) or Pd-catalyzed allylic substitution (3, 4), the mechanism is known, allowing at least a semirational approach to catalyst development. Moreover, useful general concepts have been developed during the last three decades that greatly facilitate the development of new chiral ligands, even in the absence of mechanistic information. Some of these concepts are described in the following sections, mainly from the perspective of our own research.

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Probing Electronic Effects in the Asymmetric Heck Reaction with the BIPI Ligands

Cited by 146 publications

References 11 publications

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

Changing the Palladium Coordination to Phosphinoimidazolines with a Remote Triazole Substituent

Design of Chiral Ligands for Asymmetric Catalysis: From C₂‐Symmetric P,P‐ and N,N‐Ligands to Sterically and Electronically Nonsymmetrical P,N‐Ligands

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Probing Electronic Effects in the Asymmetric Heck Reaction with the BIPI Ligands

Cited by 146 publications

References 11 publications

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)-mediated asymmetric intramolecular allylic amination

Changing the Palladium Coordination to Phosphinoimidazolines with a Remote Triazole Substituent

Design of Chiral Ligands for Asymmetric Catalysis: From C2‐Symmetric P,P‐ and N,N‐Ligands to Sterically and Electronically Nonsymmetrical P,N‐Ligands

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Design of Chiral Ligands for Asymmetric Catalysis: From C₂‐Symmetric P,P‐ and N,N‐Ligands to Sterically and Electronically Nonsymmetrical P,N‐Ligands