Regio- and Diastereoselective Tandem Rhodium-Catalyzed Allylic Alkylation/Pauson−Khand Annulation Reactions

Evans, and P. Andrew; Robinson, John

doi:10.1021/ja015531h

Cited by 173 publications

(74 citation statements)

References 12 publications

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“…A similar mode of reactions is very unlikely here because hard nucleophiles such as arylboronic acids react with the same catalyst and substrate to give retention of stereochemistry (58). A net S N 2Ј displacement of the bridgehead leaving group is observed that is also different from what is obtained with rhodium catalysts and allylic carbonates where nucleophilic attack occurs at the same carbon from which the leaving group departs (11)(12)(13)(14)(15)(16)(17). Nucleophilic attack at the carbon bearing the leaving group has also been documented with Ru (48) and Fe (44) catalysts.…”

Section: Discussionmentioning

confidence: 73%

“…The formation of the 1,2-trans products is atypical for ring opening reactions of oxabicyclic alkenes, which usually generate the syn-1,2 diastereomers via exo nucleophilic attack (1,2). Furthermore, regio-and stereochemical results diverge from previously documented rhodium-catalyzed reactions with allylic carbonates (9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The observations obtained with oxabicyclic alkenes find little precedent when compared to other allylic functionalizations including those catalyzed by Pd (refs.…”

mentioning

confidence: 89%

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Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Lautens

Fagnou²

2004

Proc. Natl. Acad. Sci. U.S.A.

103

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Catalyst and substrate studies have been performed on the rhodium-catalyzed asymmetric ring opening reaction. A working model is advanced that involves oxidative insertion with retention to form an organorhodium intermediate that then undergoes nucleophilic attack with inversion. Kinetic and competition experiments have uncovered evidence for a proton transfer step in the catalytic cycle that may activate both the allylrhodium intermediate and the nucleophile. We have also conducted experiments designed to understand which properties of the PPF-P t Bu2 ligand contribute to the high reactivities and enantioselectivities.W e have previously reported that chiral rhodium(I) catalysts induce ring opening oxa-and azabicyclic alkenes with a variety of soft nucleophiles such as alcohols, phenols, amines, anilines, malonates, and carboxylates in high yield and enantioselectivity (1-8). The products are generated by an S N 2Ј nucleophilic displacement of the bridgehead leaving group with inversion providing the 1,2-trans product as one regio-and diastereomer. The formation of the 1,2-trans products is atypical for ring opening reactions of oxabicyclic alkenes, which usually generate the syn-1,2 diastereomers via exo nucleophilic attack (1, 2). Furthermore, regio-and stereochemical results diverge from previously documented rhodium-catalyzed reactions with allylic carbonates (9-18). The observations obtained with oxabicyclic alkenes find little precedent when compared to other allylic functionalizations including those catalyzed by Pd (refs. 19 In this report we describe catalyst and substrate studies and advance a mechanistic working model that rationalizes the stereochemical outcome and other experimental observations (Scheme 1). We have also conducted experiments designed to understand the properties of the PPF-P t Bu 2 ligand that contribute to high reactivities and enantioselectivities.Experimental procedures and characterization data can be found in Supporting Text, which is published as supporting information on the PNAS web site. Ligand Studies: Variations on the Josiphos Template and Other Ligand MotifsSeveral structural elements are present on the PPF scaffold that could contribute to its successful application in these reactions (51-53). PPF has elements of central and planar chirality as well as two phosphine atoms that differ both sterically and electronically. Two methods were used to determine the influence of the ligand on the rate. In cases where a significant difference in rate was observed, percent conversion vs. time, as determined by crude 1 H NMR, was used to quantify the reactivity of the catalyst. In cases where a more precise measurement of rate was desired, kinetic runs were performed.By comparing the reactivity and enantioselectivity of ligands 3 and 4, two trends emerge (Scheme 2). First, by increasing the steric bulk ( t Bu Ͼ Cy) the enantioselectivity is increased from 88% with 3 to 96% enantiomeric excess (ee) with the bulkier t Bu 2 P ligand 4. This increase in enantioselectivity comes at ...

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Section: Discussionmentioning

confidence: 73%

mentioning

confidence: 89%

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Lautens

Fagnou²

2004

Proc. Natl. Acad. Sci. U.S.A.

103

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“…Thus, they synthesized cyclopentenone 101 from allylic acetate 99 and diethyl propargylmalonate salt in the presence of [RhClCO(dppp)] 2 with high yield. When formation of intermediate 100 was complete they just heated the reaction to 80 • C to get 101 (Scheme 29) [126].…”

Section: Scheme 28 Tandem Action Of Different Catalysts In Allylic Almentioning

confidence: 99%

Cascade Reactions Involving Pauson—Khand and Related Processes

Pérez‐Castells

2006

ChemInform

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“…In general, transition metal catalyzed cascade reactions can be categorized into two groups, either being domino reactions that constantly repeat the same elementary step [15][16][17], or they are constituted by reaction steps that consist of fundamentally different elementary transformations [18][19][20][21][22][23][24][25]. As such, transition metal catalyzed domino reactions involve organometallic intermediates which are constantly regenerated and yield complex, often polycyclic, organic products after numerous insertion steps and after a concluding elimination.…”

Section: Introductionmentioning

confidence: 99%

Sequentially Palladium-Catalyzed Processes in One-Pot Syntheses of Heterocycles

Lessing

Müller

2015

Applied Sciences

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Sequentially Pd-catalyzed processes are excellent entries to heterocycle synthesis. The broad mechanistic variety combined with often very mild reaction conditions allow the concatenation of elementary organic and organometallic steps to novel sequences in the sense of one-pot domino and multicomponent reactions. Given the numerous opportunities of alkyne coordination and their Pd-mediated transformations, alkynylation and carbometallation play a key role, both for purely organometallic sequences as well as in those processes that are intercepted by cyclocondensation. Pd-catalyzed aminations also find more and more entry into novel heterocycle syntheses based upon this theme.

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Regio- and Diastereoselective Tandem Rhodium-Catalyzed Allylic Alkylation/Pauson−Khand Annulation Reactions

Cited by 173 publications

References 12 publications

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Cascade Reactions Involving Pauson—Khand and Related Processes

Sequentially Palladium-Catalyzed Processes in One-Pot Syntheses of Heterocycles

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