Computationally Designed and Experimentally Confirmed Diastereoselective Rhodium-Catalyzed Pauson−Khand Reaction at Room Temperature

Baik, Mu‐Hyun; Mazumder, Shivnath; Ricci, Paolo F.; Sawyer, James R.; Song, Ye-Geun; Wang, Huijun; Evans, P. Andrew

doi:10.1021/ja107895g

Cited by 52 publications

(34 citation statements)

References 24 publications

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“…15 Although the chemical steps in the catalytic cycle seem identical on first sight, the oxidative addition promoted by the fivecoordinate Rh-complex is fundamentally different from the same reaction mediated by the four-coordinate Rh-analogue. Figure 6 provides an intuitive summary of the diastereoselective metallacarbocycle forming event using the five-coordinate Rhcomplex.…”

Section: ■ Discussionmentioning

confidence: 99%

Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways

et al. 2016

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A conceptual theory for analyzing and understanding oxidative addition reactions that form the cornerstone of many transition metal mediated catalytic cycles that activate C-C and C-H bonds, for example, was developed. The cleavage of the σ- or π-bond in the organic substrate can be envisioned to follow a closed or an open shell formalism, which is matched by a corresponding electronic structure at the metal center of the catalyst. Whereas the assignment of one or the other mechanistic scenario appears formal and equivalent at first sight, they should be recognized as different classes of reactions, because they lead to different reaction optimization and control strategies. The closed-shell mechanism involves heterolytic bond cleavages, which give rise to highly localized charges to form at the transition state. In the open-shell pathway, bonds are broken homolytically avoiding localized charges to accumulate on molecular fragments at the transition states. As a result, functional groups with inductive effects may exert a substantial influence on the energies of the intermediate and transition states, whereas no such effect is expected if the mechanism proceeds through the open-shell mechanism. If these functional groups are placed in a way that opens an electronic communication pathway to the molecular sites where charges accumulate, for example, using hyperconjugation, electron donating groups may stabilize a positive charge at that site. An instructive example is discussed, where this stereoelectronic effect allowed for rendering the oxidative addition diastereoselective. No such control is possible, however, when the open-shell reaction pathway is followed, because the inductive effects of functional groups have little to no effect on the stabilities of radical-like substrate states that are encountered when the bonds are broken in a homolytic fashion. Whether the closed-shell or open-shell mechanism for oxidative addition is followed is determined by the ordering of the d-orbital dominated frontier orbitals. If the highest occupied molecular orbital (HOMO) is oriented in space in such a way that will give the organic substrate easy access to the valence electron pair, the closed-shell mechanism can be followed. If the shape and orientation of the HOMO is not appropriate, however, an alternative pathway involving singlet excited states of the metal that will invoke the matching radicaloid cleavage of the organic substrate will dominate the oxidative addition. This novel paradigm for formally analyzing and understanding oxidative additions provides a new way of systematically understanding and planning catalytic reactions, as demonstrated by the in silico design of room-temperature Pauson-Khand reactions.

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Section: ■ Discussionmentioning

confidence: 99%

Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways

et al. 2016

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“…[4] The calculations predicted that changing the alkyne terminus from H to Cl would significantly lower the barrier to formation of the cis isomer by 4 kcal/mol, but not significantly reduce the barrier to formation of the trans isomer. To verify this, Evans and coworkers treated the corresponding enynes with a rhodium catalyst at room temperature (Scheme 1) and observed no reaction when the alkyne was terminal, but were able to isolate the cyclopentenone in 74% yield when substituted with chlorine.…”

Section: Achiral/racemic Processesmentioning

confidence: 99%

Recent Advances in the Pauson–Khand Reaction

Ricker

Geary

2017

Top Catal

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“…In a joint effort between the Baik and Evans groups, factors controlling the diastereoselectivity of rhodium-catalyzed Pauson-Khand reactions (Scheme 7) were discovered. [17] This understanding was parlayed into the design of new substrates predicted to undergo highly diastereoselective Pauson-Khand reactions. Quantum chemical calculations on rate-determining transition state structures leading to the major and minor products suggested that both structures are polarized, but in opposite directions.…”

Section: Predicting the Diastereoselectivity For An Organometallic Rementioning

confidence: 99%

The Many Roles of Quantum Chemical Predictions in Synthetic Organic Chemistry

Nguyen¹,

Tantillo²

2013

Chemistry An Asian Journal

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Computationally Designed and Experimentally Confirmed Diastereoselective Rhodium-Catalyzed Pauson−Khand Reaction at Room Temperature

Cited by 52 publications

References 24 publications

Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways

Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways

Recent Advances in the Pauson–Khand Reaction

The Many Roles of Quantum Chemical Predictions in Synthetic Organic Chemistry

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