Gold‐Catalyzed Intramolecular Redox Reaction of Sulfinyl Alkynes: Efficient Generation of α‐Oxo Gold Carbenoids and Application in Insertion into RCO Bonds

Li, Guotao; Zhang, Liming

doi:10.1002/anie.200701449

Cited by 270 publications

(44 citation statements)

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“…This umpolung [3] reactivity of indole has, however, only been realized in a limited number of cases. [4] For the past few years we have engaged in extensive studies of gold-catalyzed intra- [5] and intermolecular [6] alkyne oxidations using oxygen-delivering oxidants, [7] wherein reactive a-oxo gold carbene intermediates are presumably generated [8] and responsible for the diverse reaction outcomes. Lately we extended this strategy to the use of nitrene precursors as oxidants, thus providing access to reactive aimino gold carbenes (Scheme 1 a); [9] however, the chemistry has so far been limited to ynamides, [10] which are activated alkynes.…”

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confidence: 99%

Umpolung Reactivity of Indole through Gold Catalysis

Luo

Liu

et al. 2011

Angewandte Chemie

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The indole 3-position is highly electron-rich and typically functions as the primary nucleophilic site to react with a large array of electrophiles, leading to various functionalized indoles. [1] The reversal of this prime reactivity, i.e., making the indole 3-position electrophilic, would be of significant synthetic utility and provide a complementary strategy to access derivatives [2] otherwise difficult to prepare conventionally. This reactivity umpolung [3] of indole has, however, only been realized in limited cases. [4] For the past few years we have engaged in extensive studies of gold-catalyzed intra- [5] and intermolecular [6] alkyne oxidations using oxygen-delivering oxidants, [7] where reactive α-oxo gold carbene intermediates are presumably generated [8] and responsible for the diverse reaction outcomes. Lately we extended this strategy to the use of nitrene precursors as oxidants, providing access to reactive α-imino gold carbenes (Scheme 1A); [9] however, the chemistry has so far been limited to ynamides, [10] which are activated alkynes. In our effort to expand the scope of this type of gold-catalyzed nitrene transfer, [11] we decided to use an azido group as a nitrene precursor, which was inspired by previous studies of gold- [12] and platinum-catalyzed [13] pyrrole synthesis. We reasoned that closely and rigidly positioned C-C triple bonds in ortho-azidoarylalkynes might facilitate an intramolecular nitrene transfer from the azido group to the C-C triple bond. Importantly, the thus-formed gold carbene B would serve as an electrophilic indole equivalent, as depicted in its resonance form C, therefore realizing reactivity umpolung of the indole 3-position (Scheme 1B). [14] We started by using ortho-azidophenylalkyne 1a as the substrate and anisole as the nucleophile, and the initial reaction was run in toluene using Ph 3 PAuNTf 2 [15] as the catalyst. To our delight, the desired indole regioisomers 2a and 2a' were indeed formed (entry 1), confirming that the azido group could function as a nitrene precursor and a gold carbene of type B might be indeed formed; moreover, this proposed reactive intermediate seemingly reacted mainly via its cationic resonance form C [16] as no Büchner reaction, [17] i.e., the formation of cycloheptatriene products, which is characteristic of carbene chemistry, occurred. The regioselectivity on the anisole ring is consistent with an electrophilic aromatic substitution mechanism. To our surprise, the majority of the putative gold intermediate B/C reacted with the solvent toluene, yielding a mixture of regioisomers (p-3/o-3/m-3 = 41%/ 11%/8%). Although the concentration of toluene is ~190 time of that of anisole, anisole is much more nucleophilic than toluene. [18] These results indicate that intermediate C is strongly electrophilic and hence less selective. This conclusion is consistent with the ratio of NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript p-3 vs. m-3 (~5), lower than that in the case of nitration (>10), [19] suggesting that ...

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Umpolung Reactivity of Indole through Gold Catalysis

Luo

Liu

et al. 2011

Angewandte Chemie

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“…Zhang confirmed that NHC ligands proved rewarding in terms of yields in the gold‐catalyzed rearrangement of sulfinyl alkyne 7 which proceeds via an α‐oxo gold carbene intermediate (Scheme ) 11…”

Section: Improvement Of Catalysismentioning

confidence: 91%

When NHC Ligands Make a Difference in Gold Catalysis

Gatineau

Goddard

Mouriès‐Mansuy

et al. 2013

Israel Journal of Chemistry

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“…Some examples are depicted in equation (34 -36). (38) Additional evidence for the involvement of metal carbenes in these processes was obtained in the reaction of dimeric substrates with a cationic Au(I) catalyst to give disubstituted alkynes (equation 39). 33 These reactions can be explained by isomerization of the initially formed cyclopropyl gold carbene by a [1,3] …”

Section: Carbon Nucleophilesmentioning

confidence: 96%