On the Nature of the Catalytic Palladium-Mediated Elimination of Allylic Carbonates and Acetates To Form 1,3-Dienes

Takacs, James M.; Lawson, Edward C.; Clement, Francis

doi:10.1021/ja962313t

Cited by 90 publications

(44 citation statements)

References 22 publications

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“…5,17,18 In this case, the process would involve a carbopalladation step, followed by anti-dehydropalladation or by isomerization and syn-elimination. 19 However, the isomerization step requires a reversible α-hydride elimination to form a carbene intermediate, a process unknown for palladium (unlike for Pt or Ru). 20 The next possible pathway is a non-electrophilic C-2-palladation of indole (Path B), which has been proposed by Tollari 21 and Nonoyama.…”

Section: Introductionmentioning

confidence: 99%

Direct transition metal-catalyzed functionalization of heteroaromatic compounds

2007

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During the last two decades there has been considerable growth in the development of catalytic reactions capable of activating unreactive C-H bonds. These methods allow for the synthesis of complex molecules from easily available and cheaper precursors in a fewer number of steps. Naturally, the development of C-H activation methods for direct functionalization of heterocyclic molecules, invaluable building blocks for pharmaceutical and synthetic chemistry and material science, has received substantial attention as well.

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Section: Introductionmentioning

confidence: 99%

Direct transition metal-catalyzed functionalization of heteroaromatic compounds

2007

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“…In all cases, the substrate was incorporated in a cyclohexyl ring system, whereas in acyclic allylic carbonates an anti elimination mechanism has been postulated only on the base of isotope effects. [14] In this paper, we report for the first time on evidence of competing syn and anti pathways in b-PdÀH eliminations of acyclic substrates.…”

Section: Introductionmentioning

confidence: 84%

“…However, this stereochemical outcome has been challenged more recently, when palladium complexes 2 a lacking a syn-b-hydrogen atom H b were found by the groups of Tsuji, Anderson, and Takacs to undergo at least a formal anti elimination. [8,9,13,14] The explanation offered by Tsuji is based on a resubstitution of the metal in 2 a by free Pd 0 under inversion. The isomeric complex 2 b formed thereby undergoes a conven-tional syn elimination via the s-complex 3 b.…”

Section: Introductionmentioning

confidence: 99%

“…[6,7] On the other hand, a base-induced abstraction of the b-hydrogen in 3 a has been postulated to account for the anti elimination of allyl palladium complexes. [13,14] Thus the base B À attacks the hydrogen atom H a , which is in an anti orientation relative to the palladium in the complex 3 a. This type of elimination, which follows essentially an E 2 mechanism, leads to the formation of the diene 4 b, whereby the protonated base H a B is liberated and the catalyst is regenerated.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Competing syn and anti Pathways in Palladium-Catalyzed Eliminations of Acyclic Allylic Carbonates

Schwarz

Braun

1999

Chemistry - A European Journal

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Syn-and anti-configured carbonates 6 a and 6 b, available from stereoselective aldol additions and subsequent protection with methyl chloroformate, serve as probes for the elucidation of the stereochemistry of the b-PdÀH elimination. Upon treatment with [Pd(PPh 3 ) 4 ], the carbonates 6 a and 6 b give the dienes 7 a and 7 b in different ratios; the latter stereoisomer 7 b is formed as a result of p ± s ± p conversions. Both syn and anti eliminations are shown to occur as competing reactions, the former one being the strongly preferred pathway. The highly reactive [Pd{P(nBu) 3 } 4 ] catalyst, generated in situ from Pd(OAc) 2 and P(nBu) 3 causes thermodynamic control in the elimination; thus, it serves as a smooth reagent for Z ± E isomerization.

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“…Our initial research was focused on the study of solvents, concentration, and catalyst loading. However, in all the cases, the isomerization via b-hydride elimination mechanism [10] occurred giving the corresponding diene 2 exclusively.…”

Section: Introductionmentioning

confidence: 93%

Suppression of β‐Hydride Elimination in the Intramolecular Hydrocarboxylation of Alkynes leading to the Formation of Lactones

et al. 2007

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Palladium-catalyzed intramolecular cyclization of the alkynoic acids was studied which gave the five-and six-membered lactones in moderate yields. The reaction can be conducted simply by heating a toluene solution of alkynoic acids at 100 8C in the presence of catalytic amounts of PdA C H T U N G T R E N N U N G (PPh 3 ) 4 and (o-tol) 3 P. The key for this transformation is the use of phosphines, instead of carboxylic acids, as an additive. Similar to our previously developed catalytic system the use of carboxylic acid, instead of (otol) 3 P, resulted into the exclusive formation of the diene.

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On the Nature of the Catalytic Palladium-Mediated Elimination of Allylic Carbonates and Acetates To Form 1,3-Dienes

Cited by 90 publications

References 22 publications

Direct transition metal-catalyzed functionalization of heteroaromatic compounds

Direct transition metal-catalyzed functionalization of heteroaromatic compounds

Evidence for Competing syn and anti Pathways in Palladium-Catalyzed Eliminations of Acyclic Allylic Carbonates

Suppression of β‐Hydride Elimination in the Intramolecular Hydrocarboxylation of Alkynes leading to the Formation of Lactones

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