Enantioselective gold-catalyzed intermolecular [2+2] <i>versus</i> [4+2]-cycloadditions of 3-styrylindoles with <i>N</i>-allenamides: observation of interesting substituent effects

Wang, Yidong; Zhang, Peichao; Liu, Yuan; Xia, Fei; Zhang, Junliang

doi:10.1039/c5sc01827g

Cited by 107 publications

(32 citation statements)

References 89 publications

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“…Based on these promising resultsw ei nferred that the introductiono fa ne lectron-withdrawingg roup at the N-(1)-position of the indole could have significant effects on the reaction mechanism and its energetics by preventing the undesired Nalkylation (6a)a nd by increasing the electrophilicc haracter of the intermediate immonium derivative( vide infra for further mechanistic details). [15] We provedt hat, N-(Boc)-2,3-(Me) 2indole 1b is ac ompetent reactionp artner providing the desired diastereomerically pure cyclobutyl derivative 4b in 60, 73 and 89 %y ield at room temperature, À20 and À40 8C, respectively (entries 7-9 of Ta ble 1). [16] The increase of isolated yields at lower temperatures can be rationalized in terms of minimization of gold-promoted self-condensation of 2 (i.e.,d imerization or polymerization).…”

Section: Resultsmentioning

confidence: 96%

Gold(I)‐Catalyzed Dearomative [2+2]‐Cycloaddition of Indoles with Activated Allenes: A Combined Experimental–Computational Study

Ocello

Nisi

Jia

et al. 2015

Chemistry A European J

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The gold-catalyzed synthesis of methylidene 2,3-cyclobutane-indoles is documented through a combined experimental/computational investigation. Besides optimizing the racemic synthesis of the tricyclic indole compounds, the enantioselective variant is presented to its full extent. In particular, the scope of the reaction encompasses both aryloxyallenes and allenamides as electrophilic partners providing high yields and excellent stereochemical controls in the desired cycloadducts. The computational (DFT) investigation has fully elucidated the reaction mechanism providing clear evidence for a two-step reaction. Two parallel reaction pathways explain the regioisomeric products obtained under kinetic and thermodynamic conditions. In both cases, the dearomative CC bond-forming event turned out to be the rate-determining step.

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Section: Resultsmentioning

confidence: 96%

Gold(I)‐Catalyzed Dearomative [2+2]‐Cycloaddition of Indoles with Activated Allenes: A Combined Experimental–Computational Study

Ocello

Nisi

Jia

et al. 2015

Chemistry A European J

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“…The suitability of indole derivatives for taking part in cycloadditions with allenamides was also reported by Zhang and co‐workers, for the synthesis of enantiomerically enriched C4‐ and C6‐carbocycles . In particular, 3‐vinylindoles bearing different protecting groups (PGs) at the N(1)‐position underwent chemodivergent cycloaddition (i.e., [2+2] vs. [4+2]) with N ‐sulfonyl allenamides, depending on the electronic features of the PG on the nitrogen atom.…”

Section: Application In Asymmetric Catalysismentioning

confidence: 71%

N‐Allenyl Amides and O‐Allenyl Ethers in Enantioselective Catalysis

Manoni

Bandini

2016

Eur J Org Chem

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Nowadays asymmetric catalysis is an established reality in the organic synthesis community. Nevertheless, the range of applicability both in organic and in organometallic transformations is so large that seeking for new developments seems unstoppable. In this direction, from time to time a new class of "silent" organic compounds rises to prominence and creates new perspectives in the field. Allenyl amides and allenyl A personal dedication: "Asymmetric catalysis represents my personal and primary scientific contact with Prof. Achille Umani-Ronchi. He, together with his ambitious team at the Department of Chemistry 'G. Ciamician' , has contributed substantially in expanding the frontiers of this emerging field since the late 1980s/early 1990s and I took immense advantage of this stimulating environment during my early career in Bologna. The continuing stimulus and encouragement in pursuing unpredictable and non-trivial ultimate goals constitute his 'trademark' as well as personal legacy [

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“…In 2015, the [4+2] cycloaddition of 3‐styrylindoles with N ‐allenamides was reported by our group together with that of Xia (Scheme ) . When the protecting substituent of the 3‐styrylindoles was an electron‐withdrawing group, such as CO 2 Et, Ts, or Ac, chemoselective [4+2] cycloaddition took place, generating tetrahydrocarbazole derivatives 130 (both Z ‐ and E ‐isomers) with good to high ee values in the presence of H 8 ‐BINOL‐derived phosphoramidite–gold complex [{( S , R,R )‐ L8 }AuCl].…”

Section: Cycloaddition Reactionsmentioning

confidence: 93%

“…The highly chemo‐, regio‐ and enantioselective [2+2] cycloaddition of 3‐styrylindoles and N ‐tosyl allenamides 56 a was recently reported by J. Zhang, Xia, and co‐workers . The electronic nature of the N ‐substituent of 3‐styrylindoles dictated the reaction mode.…”

Section: Cycloaddition Reactionsmentioning

confidence: 94%

Gold‐Catalyzed Enantioselective Annulations

Zhang

2016

Chemistry A European J

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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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Enantioselective gold-catalyzed intermolecular [2+2] versus [4+2]-cycloadditions of 3-styrylindoles with N-allenamides: observation of interesting substituent effects

Abstract: The cycloaddition mode ([2+2] vs. [4+2]) can be unexpectedly switched by the simple modification of the N-substituent of the 3-styrylindoles.

Cited by 107 publications

References 89 publications

Gold(I)‐Catalyzed Dearomative [2+2]‐Cycloaddition of Indoles with Activated Allenes: A Combined Experimental–Computational Study

Gold(I)‐Catalyzed Dearomative [2+2]‐Cycloaddition of Indoles with Activated Allenes: A Combined Experimental–Computational Study

N‐Allenyl Amides and O‐Allenyl Ethers in Enantioselective Catalysis

Gold‐Catalyzed Enantioselective Annulations

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