Dual stereoselectivity in the nucleophilic attack on (.pi.-allyl)palladium complexes

Baeckvall, Jan E.; Nordberg, Ruth E.; Wilhelm, Didier

doi:10.1021/ja00310a025

Cited by 96 publications

(39 citation statements)

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“…It has been proposed that coordination of benzoquinone to Pd II induces acetate attack (8,17), but we find that the rate of the reaction between 2 and benzoquinone in acetic acid is independent of the benzoquinone concentration when at least 5.8 equiv. are used (Fig.…”

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confidence: 58%

Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins

Lin¹,

Labinger²,

Bercaw³

2009

Can. J. Chem.

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Several pyridine-like ligands were found to improve Pd(OAc) 2 -catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc) 2 , which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc) 2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a Pd II -olefin adduct, followed by allylic C-H activation to produce (η 3 -allyl)Pd II species. The (η 3 -allyl)Pd II intermediate undergoes a reversible acetate attack to generate a Pd 0 -(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc) 2 . No KIE is observed for the competition experiment between allylbenzene-d 0 and allylbenzene-d 5 (CD 2 =CDCD 2 C 6 H 5 ), suggesting that allylic C-H activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc) 2 .Key words: olefin, palladium catalysis, allylic C-H oxidation, p-benzoquinone, bipyrimidine.Résumé : On a observé que plusieurs ligands apparentés à la pyridine améliorent l'oxydation allylique de l'allylbenzène en acétate de cinnamyle par la p-benzoquinone dans l'acide acétique et catalysée par le Pd(OAc) 2 . On a utilisé le meilleur ligand étudié, la bipyrimidine, pour identifier le précurseur du catalyseur pour ce système, le (bipyrimidine)Pd(OAc) 2 , qui a été complètement caractérisé. Des études mécanistiques suggèrent que la réaction se produit par le biais d'une réaction de dismutation du (bipyrimidine)Pd(OAc) 2 qui conduit à la formation d'un dimère à pont bipyrimidine qui réagit avec l'oléfine pour conduire à un adduit Pd(II)-oléfine, le tout suivi de l'activation du C-H allylique conduisant à la formation de l'espèce (η 3 -allyl)Pd(II). L'intermédiaire (η 3 -allyl)Pd(II) subit une attaque réversible par l'ion acétate qui génère un adduit Pd°-(acétate d'allyle) qui réagit subséquemment avec la p-benzoquinone pour libérer l'acétate d'allyle et régénérer le (bipyrimidine)Pd(OAc) 2 . On n'observe aucun effet isotopique cinétique pour l'expérience de compétition entre l'allylbenzène-d 0 et l'allylbenzène-d 5 (CD 2 =CDCD 2 C 6 H 5 ); ce résultat suggère que l'activation allylique n'est pas l'étape cinétiquement déterminante. Les acétoxylations allyliques catalytiques du cyclohexène et d'autres oléfines terminales sont aussi affectées par le (bipyrimidine)Pd(OAc) 2 .

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contrasting

confidence: 58%

Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins

Lin¹,

Labinger²,

Bercaw³

2009

Can. J. Chem.

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“…This mechanism has been confirmed by mechanistic studies on isolated π-allylpalladium complexes [60]. Thus, in the absence of chloride ligands, a 1,4-trans-diacetoxylation occurs, whereas in the presence of a catalytic amount of chloride ions a 1,4-cisdiacetoxylation takes place.…”

Section: -Diacyloxylationmentioning

confidence: 62%

Palladium‐Catalyzed 1,4‐Additions to Conjugated Dienes

Bäckvall

2013

Metal‐Catalyzed Cross‐Coupling Reactions and More

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“…[22] [α] 20 D ϭ Ϫ29.2 (c ϭ 2.00, CHCl 3 , Ͼ 95% ee)}. [29] According to General Procedure a), (R)-12 was obtained on a 20-mmol scale in 42% yield (1.69 g, 8.4 mmol, 99% ee) as a colorless oil after flash chromatography (ethyl acetate/hexanes, 1:9). Ϫ [α] 20 D ϭ ϩ142.2 (c ϭ 1.0, CHCl 3, 99% ee) {ref.…”

Section: Tert-butyl (E)-3-methyl-2-(trifluoroacetyl)amino-4-hexenoatementioning

confidence: 99%

“…Ϫ [α] 20 D ϭ ϩ142.2 (c ϭ 1.0, CHCl 3, 99% ee) {ref. [29] [α] 20 D ϭ ϩ59 (c ϭ 0.93, CCl 4 , 44% ee)}. (1E,3R)-3-Acetoxy-1-phenyl-1-pentene [(R)-13]: [30] Enzymatic kinetic resolution [General Procedure a)] provided (R)-13 on a 16.25-mmol scale in 48% yield (1.59 g, 7.8 mmol, 95% ee) as a colorless oil after flash chromatography (ethyl acetate/hexanes, 1:9).…”

Section: Tert-butyl (E)-3-methyl-2-(trifluoroacetyl)amino-4-hexenoatementioning

confidence: 99%

Chelated Enolates of Amino Acid Esters − New and Efficient Nucleophiles for Isomerization-Free, Stereoselective Palladium-Catalyzed Allylic Substitutions

Kazmaier

Zumpe

2001

Eur. J. Org. Chem.

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Keywords: Allylic alkylation / Amino acids / Enolates / Isomerization / PalladiumChelated amino acid ester enolates were found to be suitable nucleophiles for palladium-catalyzed allylic alkylations. Unlike stabilized soft nucleophiles, the chelated enolates react under very mild reaction conditions, even at −78°C. If TFAprotected amino acid tert-butyl esters are used as nucleophiles, the anti-configured products are obtained in a highly diastereoselective fashion. This protocol is therefore a good supplement to the chelate enolate Claisen rearrangement, which gives rise to the corresponding syn products. Especially good results are obtained with allylic carbonates as substrates, as these are readily able to form the required π-allylpalladium complexes at temperatures as low as −78°C. In this temperature range, π−σ−π isomerization of the π-allyl intermediates does not play a significant role, and so applica-

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Dual stereoselectivity in the nucleophilic attack on (.pi.-allyl)palladium complexes

Cited by 96 publications

References 0 publications

Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins

Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins

Palladium‐Catalyzed 1,4‐Additions to Conjugated Dienes

Chelated Enolates of Amino Acid Esters − New and Efficient Nucleophiles for Isomerization-Free, Stereoselective Palladium-Catalyzed Allylic Substitutions

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