Chiral Brønsted Acid from a Cationic Gold(I) Complex: Catalytic Enantioselective Protonation of Silyl Enol Ethers of Ketones

Cheon, Cheol Hong; Kanno, Osamu; Toste, F. Dean

doi:10.1021/ja204331w

Cited by 114 publications

(68 citation statements)

References 51 publications

(20 reference statements)

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“…Furthermore, there is no indication that the acidity of a gold-complexed hydroxyl group approaches that of triflic acid. [31] Taken together, we can confidently rule out a mechanism for gold-catalyzed intermolecular alkoxylation involving σ-activation of the hydroxyl group by Brønsted acid. Similarly, because gold(I) is a much weaker and less oxophilic Lewis acid than is BF 3 ·OEt 2 , the sluggish dehydrative alkoxylation of ( R,E )- 11 catalyzed by BF 3 ·OEt 2 argues strongly against a mechanism for gold-catalyzed dehydrative alkoxylation involving σ-activation of the hydroxyl group by gold(I).…”

Section: Resultsmentioning

confidence: 90%

The Regio‐ and Stereospecific Intermolecular Dehydrative Alkoxylation of Allylic Alcohols Catalyzed by a Gold(I) N‐Heterocyclic Carbene Complex

Mukherjee

Widenhoefer

2013

Chemistry A European J

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A 1:1 mixture of (IPr)AuCl [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine] and AgClO4 catalyzes the intermolecular dehydrative alkoxylation of primary and secondary allylic alcohols with aliphatic primary and secondary alcohols to form allylic ethers. These transformations are regio- and stereospecific with preferential addition of the alcohol nucleophile at the γ-position of the allylic alcohol syn to the departing hydroxyl group and with predominant formation of the E stereoisomer. The minor α-regioisomer is formed predominantly through a secondary reaction manifold involving regioselective γ-alkoxylation of the initially formed allylic ether rather than via the direct α-alkoxylation of the allylic alcohol.

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Section: Resultsmentioning

confidence: 90%

The Regio‐ and Stereospecific Intermolecular Dehydrative Alkoxylation of Allylic Alcohols Catalyzed by a Gold(I) N‐Heterocyclic Carbene Complex

Mukherjee

Widenhoefer

2013

Chemistry A European J

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“…In the past few years, reports on gold-catalyzed organic transformations have increased substantially [10–29]. Homogeneous gold catalysis has proven to be a powerful tool in organic synthesis.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

Sun¹,

Xu²,

Shi³

2013

Beilstein J. Org. Chem.

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Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-π interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C-C and C-N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I) complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee. 2224

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“…[19] Alternatively, syn-sub- stitution is also consistent with a mechanism involving sactivation of the hydroxy group followed by concerted S N 2' displacement [20] and Toste et al have recently demonstrated that bis(gold) phosphine complexes are sufficiently Lewis acidic to acidify the hydroxy proton of an alcohol. [21] However, the failure of either triflic acid or BF 3 ·OEt 2 (10 mol %, 25 8C, 48 h) to catalyze the cyclization of (E)-1 g argues against a s-activation pathway for this allylic amination.…”

Section: Paramita Mukherjee and Ross A Widenhoefer*mentioning

confidence: 99%

Gold(I)‐Catalyzed Enantioselective Intramolecular Dehydrative Amination of Allylic Alcohols with Carbamates

Mukherjee

Widenhoefer

2012

Angewandte Chemie

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The transition-metal-catalyzed enantioselective amination of allylic esters and carbonates represents one of the most wellestablished routes to chiral, nonracemic allylic amines. [1] With the potential to condense synthetic sequences and reduce waste streams, the dehydrative amination of allylic alcohols as a route to enantiomerically enriched allylic amines has gained considerable interest. However, while the stereospecific amination of chiral secondary allylic alcohols has been demonstrated, [2][3][4] the enantioselective amination of allylic alcohols remains problematic. [5] Carreira et al. have reported the Ir I -catalyzed enantioselective amination of 1-cyclohexylprop-2-enol with sulfamic acid in 70 % ee. [6] Hartwig et al. have reported the Ir I /BPh 3 -catalyzed enantioselective intermolecular amination of primary allylic alcohols with aromatic amines with up to 94 % ee, but this method was restricted to cinnamyl alcohols in the absence of a stoichiometric Lewis acid promoter. [7] The groups of Yamamoto [8] and Kitamura [9] have independently reported the enantioselective intramolecular amination of allylic alcohols catalyzed by Hg II and Ru II complexes, respectively. However, these methods were restricted to sulfonamide nucleophiles and high enantioselectivity was realized only for the formation of arene-fused nitrogen heterocycles. Herein we report a gold-catalyzed protocol for the intramolecular enantioselective amination of allylic alcohols with carbamates to form five-and sixmembered aliphatic nitrogen heterocycles with up to 95 % ee.We recently reported the intramolecular dehydrative amination of allylic alcohols with alkylamines catalyzed by an achiral gold(I) phosphine complex. [4,10] Encouraged by the high efficiency and stereospecificity of this transformation and guided by both our previous work in the area of gold(I)catalyzed enantioselective allene hydroamination [11,12] and Bandinis recent demonstration of gold(I)-catalyzed enantioselective arylation [13] and alkoxylation [14] of allylic alcohols, [15] we targeted axially chiral bis(gold) complexes as catalysts for the intramolecular enantioselective amination of the ebenzylamino allylic alcohol (E)-1 a (Table 1). Unfortunately, optimization within this framework [16] proved largely unsuccessful: treatment of (E)-1 a with a catalytic 1:2 mixture of [(S)-2](AuCl) 2 and AgSbF 6 in dioxane at 25 8C for 5 h led to quantitative conversion to 2-vinylpyrrolidine 3 a, but with only 29 % ee (Table 1, entry 1). [17] We then focused our attention on the manipulation of the nitrogen nucleophile as a means to amplify stereoinduction (Table 1). These experiments proved fruitful and gold(I)-catalyzed cyclization of Fmoc-protected e-amino allylic alcohol (E)-1 g employing an optimized catalyst system comprised of [(S)-2](AuCl) 2 (2.5 mol %) and AgClO 4 (5 mol %) in dioxane at room temperature for 48 h led to the isolation of (S)-3 g in 95 % yield with 91 % ee (Table 1, entry 7). [16,18]

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Chiral Brønsted Acid from a Cationic Gold(I) Complex: Catalytic Enantioselective Protonation of Silyl Enol Ethers of Ketones

Cited by 114 publications

References 51 publications

The Regio‐ and Stereospecific Intermolecular Dehydrative Alkoxylation of Allylic Alcohols Catalyzed by a Gold(I) N‐Heterocyclic Carbene Complex

The Regio‐ and Stereospecific Intermolecular Dehydrative Alkoxylation of Allylic Alcohols Catalyzed by a Gold(I) N‐Heterocyclic Carbene Complex

Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

Gold(I)‐Catalyzed Enantioselective Intramolecular Dehydrative Amination of Allylic Alcohols with Carbamates

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