The Inner-Sphere Process in the Enantioselective Tsuji Allylation Reaction with (<i>S</i>)-<i>t</i>-Bu-phosphinooxazoline Ligands

Keith, John A.; Behenna, Douglas C.; Mohr, Justin T.; Ma, Sandy; Marinescu, Smaranda C.; Oxgaard, Jonas; Stoltz, Brian M.; Goddard, William A.

doi:10.1021/ja070516j

Cited by 141 publications

(99 citation statements)

References 21 publications

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“…12,13,14 Preliminary studies (Scheme 1) suggested that an internal mechanism (i.e. reductive elimination) is a lower-energy pathway than the corresponding external mechanism involving attack of the enolate onto an η 3 -allyl complex; it was later discovered that η 1 -allylpalladium carboxylate 5 was found to be the resting state of the catalyst and that decarboxylation was likely rate-limiting.…”

Section: Stereoablative Transformationsmentioning

confidence: 99%

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

et al. 2017

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An important subset of asymmetric synthesis is dynamic kinetic resolution, dynamic kinetic asymmetric processes and stereoablative transformations. Initially, only enzymes were known to catalyze dynamic kinetic processes but recently various synthetic catalysts have been developed. This review summarizes major advances in non-enzymatic, transition metal promoted dynamic asymmetric transformations reported between 2005 and 2015.

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Section: Stereoablative Transformationsmentioning

confidence: 99%

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

et al. 2017

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“…1c) may interact with the C3–C4 π cloud, placing the nucleophilic Cγ near the dienoate C6. This pathway would be reminiscent of a 3,3′-reductive elimination proposed vis-à-vis enantioselective allyl–allyl coupling with Ni- and Pd complexes 17,18 . A similar reaction mode with an organocopper species has been mentioned in just one instance (again, without experimental or computational support) 19 .…”

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confidence: 99%

Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups

Meng

Torker

et al. 2016

Nature

126

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Conjugate (or 1,4-) additions of carbanionic species to α,β-unsaturated carbonyl compounds are vital to research in organic and medicinal chemistry, and there are several known chiral catalysts that facilitate the catalytic enantioselective additions of nucleophiles to enoates1. However, catalytic enantioselective 1,6-conjugate additions are uncommon, and ones that are able to incorporate readily functionalizable moieties, such as propargyl or allyl groups, into acyclic α,β,γ,δ-doubly unsaturated acceptors are unknown2. Chemical transformations that could generate a new bond at the C6 position of a dienoate are particularly desirable, as the resulting products would be subjected to further modifications; such reactions, especially when dienoates contain two equally substituted olefins, are scarce3 and are confined to reactions promoted by a phosphine–copper (with alkyl Grignard4,5, dialkylzinc or trialkylaluminum compounds6,7), a diene–iridium (with arylboroxines)8,9, and a bisphosphine–cobalt catalyst (with monosilyl-acetylenes)10. 1,6-conjugate additions are otherwise limited to substrates where there is full substitution at C411. It is not clear why certain catalysts favor bond formation at C6, and – while there are a small number of catalytic enantioselective conjugate allyl additions12,13,14,15 – related 1,6-additions and processes involving a propargyl unit are non-existent. In this manuscript, we show that an easily accessible organocopper catalyst can promote 1,6-conjugate additions of propargyl and 2-boryl-substituted allyl groups to acyclic dienoates with high selectivity. A commercially available allenylboron compound or a monosubstituted allene may be used. Products can be obtained in up to 83 percent yield, >98 percent diastereo- (for allyl additions) and 99:1 enantiomeric ratio. Mechanistic details, including the origins of high site- (1,6- versus 1,4-) and enantioselectivity as a function of the catalyst structure and reaction type, have been elucidated by means of density functional theory (DFT) calculations.

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“…Initial mechanistic studies found zero-order kinetic dependence in substrate, which suggests a fast initial reaction between catalyst and substrate and a slow subsequent step, presumably either decarboxylation or protonation of the putative enolate intermediate common to both the protonation and allylic alkylation reactions with this catalyst system. 74 However, in the protonation reaction opposite enolate facial preference was observed for tetralone-and cyclohexanone-derived enolates, whereas in the alkylation reaction consistent enantiofacial selectivity was observed. 70,71,72 This unexpected result suggests a substantial difference in the bond-forming portion of the mechanism.…”

Section: Nih-pa Author Manuscriptmentioning

confidence: 97%

Enantioselective Protonation

2008

Synfacts

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Enantioselective protonation is a common process in biosynthetic sequences. The decarboxylase and esterase enzymes that effect this valuable transformation are able to control both the steric environment around the proton acceptor (typically an enolate) and the proton donor (typically a thiol). Recently, several chemical methods to achieve enantioselective protonation have been developed by exploiting various means of enantiocontrol in different mechanisms. These laboratory transformations have proven useful for the preparation of a number of valuable organic compounds.A fundamental method to generate a tertiary carbon stereocenter is to deliver a proton to a carbanion intermediate. However, enantioselective transfer of a proton presents unusual challenges, specifically, manipulating a very small atom and avoiding product racemization at a particularly labile stereocenter. As a result, the conditions for a successful enantioselective protonation protocol may be very specific to a certain substrate class. Tertiary carbon stereocenters are extremely common in valuable biologically active natural products, and thus the need for synthetically useful enantioselective methods to form these stereocenters is vital. 1In this review, we discuss several strategic approaches to enantioselective protonation. Emphasis has been placed on recently developed methods and their accompanying mechanisms in order to update the most recent prior reviews on this topic. 2,3,4,5,6,7,8 Each method relies on particular stereochemical control elements based on the mechanism of the protonation transformation. Appreciation of these controlling elements may lead to improved methods for preparing valuable chiral materials for a variety of synthetic applications. Important Factors in Achieving Enantioselective ProtonationSeveral of the most important practical features of enantioselective protonation were enumerated in Fehr's 1996 review. 2 Principal among these is the fact that enantioselective protonations are necessarily kinetic processes since under thermodynamic control racemate would be formed. Accordingly, it is often necessary to match the pK a of the proton donor and the product to prevent racemization before product isolation. It is unfortunate that the same anion stabilizing groups (e.g., ketones) that make protonations relatively easy to achieve also impart a degree of instability in the product. This has led some researchers to explore hydrogen atom transfer reactions in lieu of Brønsted acid-mediated protonations (see the subsection Enantioselective Hydrogen Atom Transfer below).Correspondence should be addressed to B.M.S. stoltz@caltech.edu. The authors declare no competing financial interests. NIH Public Access Author ManuscriptNat Chem. Author manuscript; available in PMC 2010 April 27. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn addition to the obvious challenges of product stability under the reaction conditions, the rapid rate of proton exchange in solution often leads to significant l...

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The Inner-Sphere Process in the Enantioselective Tsuji Allylation Reaction with (S)-t-Bu-phosphinooxazoline Ligands

Cited by 141 publications

References 21 publications

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups

Enantioselective Protonation

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