“Silver Effect” in Gold(I) Catalysis: An Overlooked Important Factor

Wang, Dawei; Cai, Rong; Sharma, Sripadh; Jirak, James G.; Thummanapelli, Sravan K.; Akhmedov, Novruz G.; Zhang, Hui; Liu, Xingbo; Petersen, Jeffrey L.; Shi, Xiaodong

doi:10.1021/ja303862z

Cited by 442 publications

(329 citation statements)

References 56 publications

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“…1,2 Classical Kucherov procedures for alkynes' hydration into ketones employ mercuric salt as the catalyst in aqueous sulfuric acid. 3,4 Due to the toxicity of Hg salts, many other metal-catalyzed alkyne hydration procedures have been developed, including ones catalyzed by Ru, 5 Rh, 6 Pd, 7 Pt, 8,9 Sn−W, 10 Au, [11][12][13][14][15][16][17]18,19 Ir,20,21 Co, 22 Ag, 23,24 etc. Besides various metal catalysts, Brønsted-acidcatalyzed hydration reactions also exist in the literature.…”

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confidence: 99%

Metal-Free Markovnikov-Type Alkyne Hydration under Mild Conditions

2016

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A Markovnikov-type alkyne hydration protocol is presented using 20% CF 3 SO 3 H (TfOH) as the catalyst under unprecedented mild conditions applicable to various alkynes, including terminal arylalkynes, terminal nonfunctionalized aliphatic alkynes, and internal alkynes with excellent regioselectivity in good to excellent yields (average yields >85%). The reaction procedure operates under mild conditions (25−70°C), with broad functional group compatibility, and uses only slightly more than a stoichiometric amount of water in the absence of any transition metal. The success of this protocol hinges upon the utilization of trifluoroethanol as the solvent.C onverting alkynes into carbonyl compounds through hydration, especially Markovnikov-type hydration (Scheme 1a), is a fundamental transformation in organic synthesis with 100% atom economy. 1,2 Classical Kucherov procedures for alkynes' hydration into ketones employ mercuric salt as the catalyst in aqueous sulfuric acid. 3,4 Due to the toxicity of Hg salts, many other metal-catalyzed alkyne hydration procedures have been developed, including ones catalyzed by Ru, 5 Rh, 6 Pd, 7 Pt, 8,9 Sn−W, 10 Au, [11][12][13][14][15][16][17]18,19 Ir,20,21 Co, 22 Ag, 23,24 etc. Besides various metal catalysts, Brønsted-acidcatalyzed hydration reactions also exist in the literature. 25,26 However, most of the reactions reported so far have suffered from at least one drawback: (1) high temperature (>100°C); (2) expensive noble metals (Ru, Rh, Pd, Pt, Au, Ir, Ag, etc.); (3) narrow functional group compatibility; (4) large excess of water and acidic additive besides the metal catalysts if any (Scheme 1b). Therefore, a method that could operate under mild conditions (i.e., room temperature) with broad functional group tolerance at the cost of close to a stoichiometric amount of water and a catalytic amount of acid in the absence of any transitional metal 27 would be highly desirable. In this paper, we describe such a protocol that fulfills all of these requirements (Scheme 1c).Our work was inspired by the facts that (1) vinyl (phenyl) carbocation can be strongly stabilized in CF 3 CH 2 OH (TFE) as the solvent and (2) TFE cannot react with the carbocation due to its low nucleophilicity. 28−30 Given that alkyne's hydration is generally via a vinyl carbocation intermediate, 31−34 we hypothesized that TFE's ability to stabilize a vinyl carbocation could decrease the transition state energy to form the carbocation intermediate, which may cause the hydration reaction to proceed under conditions milder than those of reactions occurring in other solvents. Besides, low Lewis basicity of TFE would not compete with the triple bond to be activated by the acid catalysts (including metal and Brønsted catalysts). To quantitatively compare the difference between TFE and other solvents, we conducted DFT calculation on the protonation step in different solvents (Figure 1). TFE and ethanol were selected as the solvents to conduct the DFT analysis comparison because these two solvents bear nearl...

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confidence: 99%

Metal-Free Markovnikov-Type Alkyne Hydration under Mild Conditions

2016

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“…The switch in the regioselectivity (entry 1 vs 5) could be associated with a non innocent presence of the silver salt. 49 This assumption was confirmed with an experiment conducted with the combination PPh 3 AuNTf 2 /AgCl as catalyst that also switched the regioselectivity to give in this case a 1.2/1 ratio of 2a/3a (entry 6). These results support the complexity of the gold/silver catalysis mechanisms pointed out by Shi.…”

Section: Resultsmentioning

confidence: 62%

“…These results support the complexity of the gold/silver catalysis mechanisms pointed out by Shi. 49 On the other hand, although a minor influence of the catalyst counterion in the outcome of the process was determined, the product ratio 2a/3a could be slightly improved using a triflate anion (entry 10 vs entries [11][12][13]. In contrast, the solvent has a crucial effect in the regioselectivity.…”

Section: Resultsmentioning

confidence: 99%

Regioselective Synthesis of Elusive 4,9-Dihydro-1H-Carbazoles by Gold-Catalyzed Cycloisomerization of 3-Allenylmethylindoles

et al. 2013

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Abstract.A general and efficient synthesis of 4,9-dihydro-1H-carbazoles from 3-allenylmethylindoles is reported. The process, catalyzed by a cationic gold(I) complex, involves a formal C2H bond activation of the indole unit by reaction with allenes. The nature of the substituents at the allylic as well as the terminal position of the allene moiety has a crucial effect on the regioselectivity of the cyclization, which is also influenced by the catalyst and the solvent employed. Moreover, some evidence of the 2 contribution of different reaction routes is provided which led us to propose a plausible multi-pathway mechanism consistent with all the results described.

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“…Intriguingly, the reactivities of the gold catalysts generated in situ in some cases differ dramatically to the Celite-filtered gold catalysts. [18] We therefore examined the effect of Celite filtration of the gold species on the desymmetrization of mesodiols 1 (Figure 1). The reactivity reduced dramatically by the filtration of the in situ generated gold catalyst through Celite (conditions B) to give yields of less than 10 %.…”

Section: Resultsmentioning

confidence: 99%

Gold(I)‐Catalyzed Asymmetric Desymmetrization of meso‐Alkynyl Diols and Kinetic Resolution of the Corresponding dl‐Diols: Effects of Celite Filtration and Silver Salts

Sota¹,

Yamamoto²,

Murai³

et al. 2015

Chemistry A European J

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The asymmetric desymmetrization of meso-2-alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salt co-catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding DL-diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso-diols is independent of the combination of axially chiral diphosphine(AuCl)2 precatalyst and silver salt co-catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)2 and silver salt. The reactivity was largely dependent on the nature of the gold(I) species.

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“Silver Effect” in Gold(I) Catalysis: An Overlooked Important Factor

Cited by 442 publications

References 56 publications

Metal-Free Markovnikov-Type Alkyne Hydration under Mild Conditions

Metal-Free Markovnikov-Type Alkyne Hydration under Mild Conditions

Regioselective Synthesis of Elusive 4,9-Dihydro-1H-Carbazoles by Gold-Catalyzed Cycloisomerization of 3-Allenylmethylindoles

Gold(I)‐Catalyzed Asymmetric Desymmetrization of meso‐Alkynyl Diols and Kinetic Resolution of the Corresponding dl‐Diols: Effects of Celite Filtration and Silver Salts

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