Strong Counteranion Effects on the Catalytic Activity of Cationic Silicon Lewis Acids in Mukaiyama Aldol and Diels−Alder Reactions

Hara, Kenji; Akiyama, Ryuto; Sawamura, Masaya

doi:10.1021/ol052206g

Cited by 108 publications

(70 citation statements)

References 18 publications

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“…The reactivity of these reagents is enhanced through incorporation of more weakly coordinating anionic ligands such as disulfonimides, as demonstrated initially by Ghosez in racemic Diels-Alder reactions (7,8,9). List and coworkers extended this advance to enantioselective catalysis through the design of chiral disulfonimide counteranion that associate with the active silylium species (10, 11).…”

Section: Main Textmentioning

confidence: 99%

Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis

Banik

Levina

Hyde

et al. 2017

Science

176

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Small molecule dual hydrogen-bond (H-bond) donors such as ureas, thioureas, squaramides, and guanidinium ions enjoy widespread use as effective catalysts for promoting a variety of enantioselective reactions. However, these catalysts are only weakly acidic, and therefore require highly reactive electrophilic substrates in order to be effective. We introduce here a mode of catalytic activity with chiral H-bond donors that enables enantioselective reactions of relatively unreactive electrophiles. Squaramides are shown to interact with silyl triflates by binding the triflate counterion to form a stable yet highly Lewis acidic complex. The silyl triflate-chiral squaramide combination promotes the generation of oxocarbenium intermediates from acetal substrates at low temperatures. Enantioselectivity in nucleophile additions to the cationic intermediates is then controlled through a network of non-covalent interactions between the squaramide catalyst and the oxocarbenium triflate.

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Section: Main Textmentioning

confidence: 99%

Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis

Banik

Levina

Hyde

et al. 2017

Science

176

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“…NMR spectra were recorded at 25 8C on JEOL Lambda 300 and JEOL Lambda 500 instruments and calibrated with tetramethylsilane (TMS) as an internal reference. All products were characterized by comparison with the reported spectral data of the authentic samples: methyl 2,2-dimethyl-3-hydroxy-3-phenylpropanoate, [14] methyl 2,2-dimethyl-3-hydroxy-5-phenylpentanoate, [15] methyl 2,2-dimethyl-3-hydroxy-5-phenyl-4-pentenoate, [16] methyl 2,2-dimethyl-3-(4-chlorophenyl)-3-hydroxypropanoate, [17] methyl 3-hydroxy-3-phenyl-2,2,3-trimethylpropanoate, [18] 4-hydroxy-4-phenylbut-1-ene. [19] Representative Mukaiyama Aldol Reaction (Table 1, entry 3) To a flask were added benzaldehyde (2a) (53.1 mg, 0.50 mmol), 1 (132.0 mg, 0.025 mmol as dimer), toluene (0.5 mL) and FC-72 (2.5 mL).…”

Section: General Remarksmentioning

confidence: 99%

Fluorous Surface‐Active Distannoxane Catalysts

Orita¹,

Tanabe²,

Ono³

et al. 2010

Adv Synth Catal

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Abstract:Fluorous distannoxanes (XR f 2 SnOSnR f 2 X) 2 ·n H 2 O (R f = C 6 F 13 C 2 H 4 ) (1: X= C 8 F 17 SO 3 , n = 10; 4: X= Cl, n = 0) (1) catalyze the Mukaiyama aldol reaction and the allylation of aldehydes with tetraallyltin at room temperature in fluorous/organic biphasic solvent systems, in which the reactions proceed more rapidly than in a single organic or fluorous solvent. Due to the unique surface activity of 1, the catalyst, organic substrate(s), and reagent(s) are distributed in both organic and fluorous phases to facilitate smooth reactions. Upon dilution with toluene after the reaction, the catalyst concentrates to the fluorous phase, while the organic substances migrate to the organic phase to effect facile catalyst recovery and recycling. By virtue of such a unique solvophilicity, a new version of fluorous biphase technology has been developed.

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“…For example, the groups of Ozerov as well as Müller have independently reported the defluorination of fluoro-and perfluoro-alkyl groups by using silylium ions [13][14][15]. Moreover, Sawamura implemented a silylium ion as Lewis acid catalyst in Mukaiyama aldol and Diels-Alder reactions [16]. Catalytic C-C bond forming reactions have also been reported [17,18].…”

Section: Introductionmentioning

confidence: 99%

Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

2016

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Novel silylium ions with N-heterocyclic imines were successfully synthesized. The reaction of trimethylsilyl imidazolin-2-imine Me 3 SiNIPr (NIPr = bis(2,6-diisopropylphenyl)-imidazolin-2-imino) with B(C 6 F 5 ) 3 leads to dimeric imino-substituted silylium ions through a methyl group abstraction on the silicon atom. Meanwhile, the intermolecular imino-coordinated silylium ion is formed by using the less sterically crowded imine Me 3 SiNItBu (NItBu = bis(tert-butyl)-imidazolin-2-imino).

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Strong Counteranion Effects on the Catalytic Activity of Cationic Silicon Lewis Acids in Mukaiyama Aldol and Diels−Alder Reactions

Abstract: [chemical reaction: see text]. A toluene-coordinated silyl borate, [Et3Si(toluene)]B(C6F5)4, demonstrated catalytic activities significantly higher than those of Me3SiOTf and Me3SiNTf2 in Mukaiyama aldol and Diels-Alder reactions.

Cited by 108 publications

References 18 publications

Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis

Lewis acid enhancement by hydrogen-bond donors for asymmetric catalysis

Fluorous Surface‐Active Distannoxane Catalysts

Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

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