Gold(I)‐Catalyzed 6‐<i>endo</i>‐Dig Hydrative Cyclization of an Alkyne‐Tethered Ynamide: Access to 1,6‐Dihydropyridin‐2(3<i>H</i>)ones

Ghosh, Nayan; Nayak, Sanatan; Sahoo, Akhila K.

doi:10.1002/chem.201301599

Cited by 78 publications

(20 citation statements)

References 81 publications

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“…Sahoo 35 developed Au(I)-catalyzed hydrative cyclization of easily accessible 5-yne-ynamides 153 , giving substituted 1,6-dihydropyridin-2(3 H )ones 157 in good to excellent yields (Scheme 28). A mechanism involving a 6- endo-dig cyclization of intermediate 155 was proposed.…”

Section: Transition Metal Mediated Cyclizationsmentioning

confidence: 99%

Ynamides in Ring Forming Transformations

et al. 2013

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Conspectus The ynamide functional group activates carbon-carbon triple bonds through an attached nitrogen atom that bears an electron-withdrawing group. As a result, the alkyne has both electrophilic and nucleophilic properties. Through the selection of the electron-withdrawing group attached to nitrogen chemists can modulate the electronic properties and reactivity of ynamides, making these groups versatile synthetic building blocks. The reactions of ynamides also lead directly to nitrogen-containing products, which provides access to important structural motifs found in natural products and molecules of medicinal interest. Therefore, researchers have invested increasing time and research in the chemistry of ynamides in recent years. This Account surveys and assesses new organic transformations involving ynamides developed in our laboratory and in others around the world. We showcase the synthetic power of ynamides for rapid assembly of complex molecular structures. Among the recent reports of ynamide transformations, ring-forming reactions provide a powerful tool for generating molecular complexity quickly. In addition to their synthetic utility, such reactions are mechanistically interesting. Therefore, we focus primarily on the cyclization chemistry of ynamides. This Account highlights ynamide reactions that are useful in the rapid synthesis of cyclic and polycyclic structural manifolds. We discuss the mechanisms active in the ring formations and describe representative examples that demonstrate the scope of these reactions and provide mechanistic insights. In this discussion we feature examples of ynamide reactions involving radical cyclizations, ring-closing metathesis, transition metal and non-transition metal mediated cyclizations, cycloaddition reactions, and rearrangements. The transformations presented rapidly introduce structural complexity and include nitrogen within, or in close proximity to, a newly formed ring (or rings). Thus, ynamides have emerged as powerful synthons for nitrogen-containing heterocycles and nitrogen-substituted rings, and we hope this Account will promote continued interest in the chemistry of ynamides.

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Section: Transition Metal Mediated Cyclizationsmentioning

confidence: 99%

Ynamides in Ring Forming Transformations

et al. 2013

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“…[6][7][8][9] Many methods have been developed in order to prepare these functionalized skeletons. [13][14][15][16][17][18][19] In 2014, Davies et al 20 reported that the gold(I)catalyzed [2 + 3] dipolar cycloaddition of electron-rich alkynes with pyridinium N-(heteroaryl)aminides gave imidazo-fused heteroaromatics in excellent yields in 1,4-dioxane solution at 90 C (Scheme 1). [10][11][12] Gold-catalyzed dipolar cycloadditions have been widely investigated and have proven to be successful in the synthesis of various fused imidazo [1,2-a] heterocycles.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the gold(i)-catalyzed synthesis of imidazo-pyrimidines and imidazo-pyrazines via [3 + 2] dipolar cycloaddition: a DFT study

Zhang

Geng

2016

RSC Adv.

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Density functional theory calculations have been carried out to study the mechanisms of gold(I)-catalyzed [3 + 2] cycloaddition reactions of pyridinium N-(heteroaryl)-aminides, as nucleophilic nitrenoids, with electron-rich alkynes, leading to imidazo-pyrimidines and imidazo-pyrazines. The calculation results suggest that the reaction mainly involves two plausible pathways leading to different products, since two carbon atoms of the asymmetric alkyne are attacked selectively by the aminide nitrogen atom. These reaction steps include C-C bond activation of the alkyne by the gold complex, a bimolecular nucleophilic attack, a closed-loop process and migration of the pyridine molecule to finally give cycloaddition products. The closed-loop process is the rate-limiting step for the whole catalytic reaction and the energy barrier shows that the pathway of the nucleophile onto the amide carbon atom of the alkyne with the electron-withdrawing group is favored. Through a detailed mechanistic investigation, we have explained the regioselectivity and the major/minor products observed by Davies et al. in gold(I)catalyzed [3 + 2] cycloaddition reactions of nucleophilic nitrenoids with electron-rich alkynes. Fig. 3 Free energy profiles calculated for the gold-catalyzed [2 + 3] cycloaddition of pyridinium N-(2-pyrimidinyl) aminide with thiophen-2ynamide. The relative free energies are given in kcal mol À1 . This journal is View Article Online found for b-TS2 in comparison to that for a-TS2 may be owing to the effect of the thienyl group. The next step for pyridine migration results in the new Au imidazole intermediate, b-IN3.Then, b-IN3, through a barrier-free process, easily generates the nal product (P3), regenerating the catalyst (CA). The whole catalytic cycle is exothermic by À65.2 kcal mol À1 . Fig. 4 Fully optimized structures of the intermediates and the transition states for pathway b are shown in Fig. 3, with selected bond lengths inÅ. The H atoms in structures are omitted for clarity. 62104 | RSC Adv., 2016, 6, 62099-62108 This journal is

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“…Of particular interest, a hydrative cyclization took place in wet 1,2‐dichloroethane, providing ketone 9 . Whereas a few Au‐catalyzed hydrative cyclizations have been described,15 such a reaction has, to the best of our knowledge, been reported only once with PtCl 4 as catalyst 16. Beyond its synthetic interest, this reaction demonstrates the compatibility of the Au/Cu catalytic system with water.…”

Section: Resultsmentioning

confidence: 82%

Silver‐Free Two‐Component Approach in Gold Catalysis: Activation of [LAuCl] Complexes with Derivatives of Copper, Zinc, Indium, Bismuth, and Other Lewis Acids

Fang

Presset

Guérinot

et al. 2014

Chemistry A European J

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Complexes of type [LAuCl] (L = phosphine, phosphite, NHC and others) are widely employed in homogeneous catalysis, however, they are usually inactive as such and must be used jointly with a halide scavenger. To date, this role has mostly been entrusted to silver salts (AgSbF6 , AgPF6, AgBF4, AgOTf, etc.). However, silver salts can be the source of deactivation processes or side reactions, so it is sometimes advisable to use silver-free cationic gold complexes, which can be difficult to synthesize and to handle compared with the more robust chloride. We show in this study that various Lewis acids of the transition and main group metal families are expedient substitutes to silver salts. We have tested Cu(I), Cu(II), Zn(II), In(III), Si(IV), Bi(III), and other salts in a variety of typical Au(I)-catalyzed transformations, and the results have revealed that [LAuCl] can form active species in their presence.

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Gold(I)‐Catalyzed 6‐endo‐Dig Hydrative Cyclization of an Alkyne‐Tethered Ynamide: Access to 1,6‐Dihydropyridin‐2(3H)ones

Cited by 78 publications

References 81 publications

Ynamides in Ring Forming Transformations

Ynamides in Ring Forming Transformations

Mechanism of the gold(i)-catalyzed synthesis of imidazo-pyrimidines and imidazo-pyrazines via [3 + 2] dipolar cycloaddition: a DFT study

Silver‐Free Two‐Component Approach in Gold Catalysis: Activation of [LAuCl] Complexes with Derivatives of Copper, Zinc, Indium, Bismuth, and Other Lewis Acids

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