Ring Expansion and 1,2‐Migration Cascade of Benzisoxazoles with Ynamides: Experimental and Theoretical Studies

Vanjari, Rajeshwer; Dutta, Shubham; Prabagar, B.; Gandon, Vincent; Sahoo, Akhila K.

doi:10.1002/asia.201901251

Cited by 23 publications

(19 citation statements)

References 71 publications

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“…The formation of a keteniminium complex, and not a πcomplex, is consistent with the Au(I)-catalyzed functionalization of ynamides in previous DFT studies. [26] It should be noted that two structural conformers could be formed from IN1A. When the isoxazole unit is inclined towards the Ms group, the TS for the C2À N bond formation is located as TS1A' with a barrier of 12.0 kcal/mol to generate iminium IN2A'.…”

Section: Resultsmentioning

confidence: 99%

Mechanism and Origins of Product Selectivity of Au‐Catalyzed Coupling Benzisoxazoles with Ynamides: A Computational Study

Rong

Zhang

et al. 2020

ChemCatChem

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Au(I)-catalyzed coupling of benzisoxazoles and ynamides was recently reported to synthesize challenging indoloquinoline core structures. In this report, we employed DFT methods to elucidate the mechanistic details of this reaction. The results reveal that the catalytic cycle involves initial coupling of ynamide with benzisoxazole, simultaneous ring opening of the isoxazole unit and attack of the dimethoxybenzene (DMOB) unit to gold carbenoid, proton transfer from the DMOB group to hydroxyl group, thioether migration, ring closure, and proton transfer. The experimentally observed ligand-controlled product selectivity is reproduced well by the calculations. The product selectivity-determining step is the ring opening of the isoxazole unit. The flexible P(t-Bu) 2 (o-biphenyl) ligand facilitates the approach of the DMOB group to gold carbenoid, which brings about significant CÀ H/π interactions in the transition state for ring opening, and thus leads to the indoloquinoline product. The rigid 1,3-bis(diisopropylphenyl)imidazol-2-ylidene ligand prefers keeping the DMOB group away from the gold carbenoid, which can cause strong orbital interaction in the transition state for ring opening, and thus results in indole product.

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Section: Resultsmentioning

confidence: 99%

Mechanism and Origins of Product Selectivity of Au‐Catalyzed Coupling Benzisoxazoles with Ynamides: A Computational Study

Rong

Zhang

et al. 2020

ChemCatChem

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“…Interestingly, it has been shown by the groups of R.-S. Liu, 45 Y. Liu, 46 and Sahoo and Gandon 47 that utilizing the isomeric 1,2-benzisoxazoles instead of anthranils (2,1-benzisoxazole) leads to a different reactivity mode upon nucleophilic attack of ynamides (Scheme 15). Formal [5 + 1] or [5 + 2] annulations are possible between ynamides 48 and 1,2-benzisoxazoles 49 depending on the nature of the gold catalyst.…”

Section: Ynamidesmentioning

confidence: 99%

Gold-Catalyzed Reactions of Specially Activated Alkynes, Allenes, and Alkenes

et al. 2020

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This review describes the gold-catalyzed reactions of specially activated alkynes, allenes, and alkenes. Such species are characterized by the presence of either electron-donating or electron-withdrawing groups as substituents of the carbon π-system. They are intrinsically polarized, and when compared to their nonspecially activated counterparts can therefore be involved in gold-catalyzed transformations featuring increased regio-, stereo-, and chemoselectivities. The chemistry of specially activated carbon π-systems under homogeneous gold catalysis is extremely rich and varied. The reactivity observed with nonspecially activated unsaturated systems can often be transposed to specially activated ones without loss of efficiency. However, specially activated carbon π-systems also exhibit specific reactivities that cannot be attained with regular substrates. In this family of carbon π-systems, ynamides and their analogs, along with alkynyl carbonyl derivatives, are the classes of substrates that have retained the most attention. This review provides an overview of the chemistry developed with all classes of specially activated carbon π-systems by discussing their general and specific reactivities, presenting and commenting on their gold-catalyzed transformations as well as their applications.

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“…). [110] Liu and co-workers reported the synthesis of pharmacologically relevant indolizine derivatives via a gold-catalyzed bicyclic annulation of 4-methoxy-1,2-dienyl-5-ynes with isoxazoles proceeding via an Au-π-allene intermediate (Scheme 78). [111] 1,4- alkyne migration of the gold π-allene intermediate led to the formation of a vinyl gold carbene intermediate which is trapped by the isoxazole to form Z-3-imino-2-en-1-al which on further cyclization yields the indolizine derivative.…”

Section: Au-catalyzed Ring Opening Reactionsmentioning

confidence: 99%

Transition Metal‐Mediated Functionalization of Isoxazoles: A Review

2021

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Isoxazoles are an important class of heterocycles with nitrogen and oxygen in a 1,2-relationship. They find wide applications in synthetic organic chemistry and are part of several drug molecules. Since the last two decades, great progress has been achieved in the synthesis and functionalization of isoxazoles, in which transition metal catalysis played a pivotal role towards achieving this goal. In particular, the transition metal (TM)-mediated site-selective functionalizations of isoxazoles which retain the pharmacologically and synthetically valuable isoxazole skeleton, are highly appealing. This comprehensive review is solely dedicated to the TM-mediated functionalization of isoxazoles, wherein we have included isoxazoles as directing groups (DG) for TM-catalyzed CÀ H functionalization reactions, TM-catalyzed direct CÀ H functionalization, along with cross-coupling reactions of isoxazoles, TM-catalyzed annulation reactions of isoxazoles and finally ring-opening reactions of isoxazoles under TMcatalysis are also discussed. Also, incorporated are discussions on reaction designs, their advantages and limitations, mechanistic details and challenges that need to be addressed to inspire synthetic organic and medicinal chemists to explore new reaction arenas and make use of this key scaffold.Scheme 1. Synthetic approaches for functionalized isoxazoles.Scheme 2. Functionalization of isoxazoles via the 4-isoxazolyl anion species.

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Ring Expansion and 1,2‐Migration Cascade of Benzisoxazoles with Ynamides: Experimental and Theoretical Studies

Cited by 23 publications

References 71 publications

Mechanism and Origins of Product Selectivity of Au‐Catalyzed Coupling Benzisoxazoles with Ynamides: A Computational Study

Mechanism and Origins of Product Selectivity of Au‐Catalyzed Coupling Benzisoxazoles with Ynamides: A Computational Study

Gold-Catalyzed Reactions of Specially Activated Alkynes, Allenes, and Alkenes

Transition Metal‐Mediated Functionalization of Isoxazoles: A Review

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