Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(i) catalyst

Campbell, Matthew; Toste, F. Dean

doi:10.1039/c1sc00160d

Cited by 116 publications

(40 citation statements)

References 71 publications

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“…This striking contrast results clearly manifest that Au δ + species exists in the reaction system with MIL‐101‐SA‐Au δ + , and the oxidation process of Au 0 to Au δ + does not take place for MIL‐101‐SA‐Au 0 during the reaction. We propose that the reaction mechanism of MIL‐101‐SA‐Au δ + might be similar to that with cationic gold under homogeneous conditions (Scheme S2, Supporting Information) . The CH bond of the alkyne is activated by Au δ + to give a gold acetylide intermediate (I) which reacts with immonium ion (II), generated from the condensation of aldehyde and amine, to afford the corresponding propargylamine (III) and regenerate the catalytic site.…”

Section: Methodsmentioning

confidence: 99%

Oxidation or Reduction State of Au Stabilized by an MOF: Active Site Identification for the Three‐Component Coupling Reaction

Yang

Jiang

2018

Small Methods

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and alkyne (also called A 3 coupling) is a representative type of CH bond activation reaction to produce propargylamine and its derivatives, serving as an important intermediate for the synthesis of many nitrogen-containing biological and pharmaceutical compounds, which can be catalyzed by Au 0 and Au δ+ (δ > 0, representing the oxidation state of Au species) according to the previous reports. [8][9][10][11][12] For example, Liu et al. sythesized an Au/MIL-53(Al) catalyst-containing Au 0 and Au 3+ species, which display good activity for the A 3 coupling reaction. [13] In addition, Liu et al. also demonstrated the Au 3+ -containing catalyst, IRMOF-3-LA-Au, can exhibit good performance in the A 3 coupling reaction. [14] Some comparative studies have been attempted, such as the contrastive properties of gold salts and Au 0 sponges, or the activity comparison between Au NPs/PMO (PMO = periodic mesoporous organosilica) and Au(PPh 3 )Cl. [15,16] Unfortunately, these comparisons have not been able to exactly give the intrinsic property of different Au species due to the presence of different supports, which is a potential factor to affect the activity. There is still an intensive debate on the nature of the gold species involved in the reaction after the elimination of the support effect. Therefore, it is necessary to seek for a suitable model with the only difference in Au oxidation state to identify the efficient active site.As a relatively new class of crystalline porous materials, metal-organic frameworks (MOFs), featuring high porosity, structural diversity, and tailorability are attracting extensive interest and are employed toward various applications including gas storage and separation, drug delivery, sensing, catalysis, etc. [17][18][19][20][21][22][23][24][25] MOFs exhibit an unrivalled ability to realize atom-level structural determination and tailoring. Particularly, some particular functional groups with strong chelating/anchor ability can be facilely grafted onto the MOF pore walls via either onestep assembly or postsynthetic modification (PSM). [26][27][28] This character makes MOFs might be ideal supports to stabilize Au 0 and Au δ+ for studying structure-catalytic activity relationship.With the above considerations in mind, we rationally introduced the salicylaldehyde (SA) and HAuCl 4 precursors into a mesoporous MOF, MIL-101-NH 2 , via a PSM approach. SA was bound to the MOF via the reaction with the amino group to give corresponding product (denoted as MIL-101-SA) with imine As one of the most efficient catalysts for the three-component coupling reaction of aldehyde, amine, and alkyne (A 3 coupling), Au has attracted extensive attention, but there is a debating issue on whether Au δ+ (δ > 0, representing the oxidation state of Au species) or Au 0 is the better active site. According to previous reports, both Au δ+ and Au 0 can catalyze the A 3 coupling reaction. Therefore, the establishment of a suitable comparison model to identify the better active site is highly desired. In this work, an ideal m...

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Section: Methodsmentioning

confidence: 99%

Oxidation or Reduction State of Au Stabilized by an MOF: Active Site Identification for the Three‐Component Coupling Reaction

Yang

Jiang

2018

Small Methods

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“…A three-component enantioselective synthesis of cyclic carbamimidates was reported in 2011 by Toste et al [125] (Scheme 31). The proposed mechanism proceeds through gold acetylide addition to the imine, followed by reaction of the isocyanate and subsequent cyclization.…”

Section: Scheme 29 Synthesis Of Enantioenriched Bis(indoyl)tetrahydromentioning

confidence: 96%

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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“…Attracted by the distinctive multiple activation modes of cationic gold(I) catalyst, in 2011 Toste and Campbell developed an enantioselective three‐component annulation of imines 440 , terminal alkynes 441 , and p ‐toluenesulfonyl isocyanate ( p ‐TsNCO) 442 by fully exploiting the carbophilic π‐acidity of the gold cation to install chiral cyclic carbamimidates 443 . From a mechanistic point of view, the cationic gold(I) species initially activated the alkynes 441 toward deprotonation with simultaneous protonation of the imines 440 , leading to the formation of electrophilic iminium 444 .…”

Section: Other Miscellaneous Reactionsmentioning

confidence: 99%

Gold‐Catalyzed Enantioselective Annulations

Zhang

2016

Chemistry A European J

221

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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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Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(i) catalyst

Cited by 116 publications

References 71 publications

Oxidation or Reduction State of Au Stabilized by an MOF: Active Site Identification for the Three‐Component Coupling Reaction

Oxidation or Reduction State of Au Stabilized by an MOF: Active Site Identification for the Three‐Component Coupling Reaction

Enantioselective Gold-Catalyzed Synthesis of Heterocyclic Compounds

Gold‐Catalyzed Enantioselective Annulations

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