Gold‐Catalyzed Asymmetric Allylic Substitution of Free Alcohols: An Enantioselective Approach to Chiral Chromans with Quaternary Stereocenters for the Synthesis of Vitamin E and Analogues

Uria, Uxue; Vila, Carlos; Lin, Ming‐Yuan; Rueping, Magnus

doi:10.1002/chem.201403768

Cited by 38 publications

(11 citation statements)

References 89 publications

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“…For the synthesis of the chiral chroman motifs, a variety of enantioselective approaches have been described . For years, a great deal of attention has focused on asymmetric synthesis that relies on transition metal-catalyzed Wacker-type or allylic substitution processes . However, the construction of chiral chroman frameworks via direct inert C–H oxidation strategy has not been reported, yet .…”

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confidence: 99%

Asymmetric Allylic C–H Oxidation for the Synthesis of Chromans

et al. 2015

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An enantioselective intramolecular allylic C-H oxidation to generate optically active chromans has been accomplished under the cooperative catalysis of a palladium complex of chiral phosphoramidite ligand and 2-fluorobenzoic acid. Mechanistic studies suggest that this reaction commences with a Pd-catalyzed allylic C-H activation event and then undergoes asymmetric allylic alkoxylation. The synthetic significance of the method has been embodied by concisely building up a key chiral intermediate to access (+)-diversonol.

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confidence: 99%

Asymmetric Allylic C–H Oxidation for the Synthesis of Chromans

et al. 2015

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“…Bandini et al demonstrated the feasibility of a cascade reaction, with gold-catalyzed alkyne hydroamination followed by the typical allylic alcohol activation [77]. Finally, the enantioselective total synthesis of α-and γ-tocopherol (vitamin E family members) was realized by Rueping et al in 2014, utilizing this strategy [78]. In many of these cases, the starting olefin geometry of the substrate is important, with the other isomer generally giving reduced yield and ee.…”

Section: Intramolecular Cyclizationsmentioning

confidence: 97%

Enantioselective Gold-Catalyzed Synthesis of Heterocyclic Compounds

Miles

Toste

2015

Topics in Heterocyclic Chemistry

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Asymmetric gold-catalyzed syntheses of a diverse range of heterocycles are described herein. This chapter outlines efforts toward the construction of these molecules via intermolecular, intramolecular, and tandem cyclization strategies. Additionally, asymmetric hydrogenation and epoxidation approaches are detailed. These methodologies generally utilize substrates containing soft, unsaturated carbon-carbon bonds, which can easily interact with the carbophilic gold atom(s). Mostly through the use of bis-or monophosphine ligands, modest to excellent yields and enantioselectivities are obtained for a variety of partially and fully saturated heterocycles. Although steric variation of the phosphine catalyst is the most commonly used strategy for enantioinduction, the use of chiral counteranions has proven useful for more challenging transformations. This chapter includes only examples of syntheses where a chiral gold catalyst is used in the direct formation of the heterocycle; examples of pendant functionalization of an existing heterocycle or chirality transfer from enantioenriched substrate to product are not included.

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“…Gold‐catalyzed asymmetric dehydrative hydroalkoxylation of allylic alcohol ( E )‐ 229 for preparation of chiral vinyl chroman 230 was reported by Rueping and co‐workers in 2014 (Scheme ) . By treating the substrates with a 1:2 catalytic mixture of [( R )‐dm‐segphos(AuCl) 2 ] and AgOTf in toluene at room temperature, the desired multisubstituted vinyl chromans 230 were obtained in moderate to high yields with good ee values.…”

Section: Cyclization Of C−c Multiple Bonds With Tethered Nucleophilesmentioning

confidence: 99%

Gold‐Catalyzed Enantioselective Annulations

Zhang

2016

Chemistry A European J

215

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Non-oxidative,regioselective,and convergent access to densely functionalized oxazoles is realized in af unctional-group tolerant manner using alkynyl thioethers.S ulfur-terminated alkynes provideaccess to reactivity previously requiring strong donor-substituted alkynes such as ynamides.Sulfur does not act in an analogous donor fashion in this gold-catalyzed reaction, thus leading to complementary regioselective outcomes and addressing the limitations of using ynamides. Compared to other heteroatom-substituted alkynes,alkynyl thioethers are remarkably little explored in intermolecular late-transition-metal catalysis,d espite being readily accessed and robust. [1, 2] Ynamides,i nc ontrast, are privileged sub-strates:i np-acid catalysis their donor nature aids metal-alkyne coordination and affords highly polarized electro-philes,t hus providing the high chemo-and regioselectivity required for the discovery of efficient intermolecular reactions (Scheme 1a). [3,4] As the resulting inclusion of ad onor-nitrogen atom limits the utility of the products,r etaining the reactivity profile of these transformations whilst accessing more flexible and readily elaborated substitution patterns would be desirable.T he value of sulfur-substituted compounds [5] coupled with progress in C À Ca nd C-heteroatom bond formation from CÀSbonds, [6] renders alkynyl thioethers appealing alternatives to ynamides.I ndeed the ketenethio-nium pathway (Scheme 1a)f rom alkynyl thioethers has recently been invoked in proton-catalyzed reactions with nitriles [2g,h] and gold-catalyzed reactions with sulfides. [2i] Ynamides enabled the discovery of formal [3+ +2] dipolar cycloadditions with nucleophilic nitrenoids, [7] thus allowing intermolecular access to a-imino gold carbene-type reactivity for heterocycle synthesis (Scheme 1b). [8, 9] Such reactions, which do not depend on ynamides,a re scarce. [8b,h] As trong donor alkyne substituent proved critical in the formation of oxazoles using N-acyl pyridinium N-aminides,aselectron-rich alkynes such as anisole derivatives did not react (Scheme 1b, inset). [8a,b] Oxazoles are valuable synthetic intermediates [10,11] and structural components in bioactive natural products, [12] agrochemicals, [13] ligands, [14] and functional materials. [15] Despite recent advances,asingle modular and convergent route to trisubstituted oxazoles,which provides the structural and functional-group diversity needed across the 2-, 4-, and 5-positions,r emains unrealized. [16] Following our interest in the use of gold catalysis with sulfides [17] we report here on the reactivity of alkynyl thioethers with nucleophilic nitrenoids to prepare oxazoles. Importantly,t he regioselectivity is not consistent with ac on-trolling ketenethionium species.T he sulfur group plays an alternative role in enabling reactivity,t hus proving complementary to donor-enabled approaches. Ther eaction of the alkynyl thioether 1a and aminide 2a (Table 1) showed that conversion into the oxazole 3 was possible at 125 8 8Ci n1 ,2-dichlorobenzene (1,2-DCB;s ...

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Gold‐Catalyzed Asymmetric Allylic Substitution of Free Alcohols: An Enantioselective Approach to Chiral Chromans with Quaternary Stereocenters for the Synthesis of Vitamin E and Analogues

Cited by 38 publications

References 89 publications

Asymmetric Allylic C–H Oxidation for the Synthesis of Chromans

Asymmetric Allylic C–H Oxidation for the Synthesis of Chromans

Enantioselective Gold-Catalyzed Synthesis of Heterocyclic Compounds

Gold‐Catalyzed Enantioselective Annulations

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