Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon

Shaw, Scott A.; Alemán, Pedro; Christy, Justin P.; Kampf, Jeff W.; Va, Porino; Vedejs, E.

doi:10.1021/ja056150x

Cited by 220 publications

(84 citation statements)

References 87 publications

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“…[70] Recent reports have further expanded this method to furanones, benzofuranones, and oxindoles, thus making it a general method for the generation of quaternary carbon stereocenters. [71] In related work, it was shown that silyl ketene acetals and silyl ketene imines are also capable of intercepting N-acylpyridinium ion intermediates, further highlighting the utility of Lewis base catalysis for the generation of quaternary carbon stereocenters. [72] Novel extensions of this general reaction class are found with variations of the nucleophile structure (Scheme 12).…”

Section: Extending the Electrophilic Reactivity Of Acylated Lewismentioning

confidence: 99%

Lewis Base Catalysis in Organic Synthesis

2008

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The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Brønsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

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Section: Extending the Electrophilic Reactivity Of Acylated Lewismentioning

confidence: 99%

Lewis Base Catalysis in Organic Synthesis

2008

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“…[70] In neueren Arbeiten wurde das Verfahren auf Furanone, Benzofuranone und Oxindole angewendet und als allgemeine Methode zum Aufbau quartärer Kohlenstoffchiralitätszentren etabliert. [71] In einer ähnlichen Arbeit wurde beschrieben, dass N-Acylpyridiniumionen auch durch Silylketenacetale und Silylketenimine abgefangen werden können; dabei werden ebenfalls durch Lewis-Base-Katalyse quartäre Kohlenstoffchiralitätszentren gebildet. [72] Neuartige Anwendungen dieser allgemeinen Reaktion betreffen Nucleophile mit anderen Strukturen (Schema 12).…”

Section: Umfang Des Aufsatzesunclassified

Lewis‐Base‐Katalyse in der organischen Synthese

2008

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Das Erbe von Gilbert Newton Lewis (1875–1946) ist im Wörterbuch der chemischen Bindung und Reaktivität allgegenwärtig. Die Bedeutung seines Konzepts der Donor‐Akzeptor‐Bindung kommt in den eponymen Grundbegriffen für Elektronenpaarakzeptoren (Lewis‐Säuren) und ‐donoren (Lewis‐Basen) zum Ausdruck. Lewis erkannte, dass Säuren nicht automatisch Wasserstoff enthalten müssen (Brønsted‐Säuren) und trug so zum Sturz des “modernen Protonenkults” bei. Seine Entdeckung läutete zunächst die Entwicklung von Lewis‐Säuren als Reagentien und Katalysatoren für organische Reaktionen ein, in den letzten Jahren wurde aber offensichtlich, dass für diese Zwecke auch Lewis‐Basen eingesetzt werden können. Bezüglich der Beschleunigung chemischer Reaktionen ergänzen Lewis‐Basen die entsprechenden Lewis‐Säuren nicht nur elektronisch: Tatsächlich können Lewis‐Basen die Elektrophilie wie auch die Nucleophilie der Verbindungen verstärken, an die sie gebunden werden. Diese unterschiedliche Reaktivität resultiert in einer bemerkenswerten Vielfalt Lewis‐Base‐katalysierter Reaktionen.

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“…When the reaction was conducted in the absence of NMM, 4a was formed in a low yield (4%) with the recovery of 3a (96%), and 5a was not formed at all, indicating that a base is essential for the completion of cyclodehydration. [12][13][14][15] On the basis of the assumption that the yield of oxazole derivative 5a could be decreased by the separation of relatively lipophilic 4a from water-soluble DMT-MM, we conducted the reaction in a biphasic solvent system composed of CH 2 Cl 2 -acetone-H 2 O (1 : 1 : 1). As a result, the yield of 5a decreased Regular Article…”

Section: Resultsmentioning

confidence: 99%

One-Pot Preparation of Oxazol-5(4<i>H</i>)-ones from Amino Acids in Aqueous Solvents

Fujita

Kunishima

2012

CHEMICAL & PHARMACEUTICAL BULLETIN

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A method for one-pot synthesis of oxazol-5(4H)-ones has been developed using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), which is available for the activation of carboxylic acids in an aqueous solvent. The oxazolones were prepared by the N-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids by the addition of N,N-diethylaniline. Since both these reactions proceed effectively with the same coupling reagent, DMT-MM, in aqueous solvents, the procedure is simplified and becomes easy to perform. In addition, 5-(triazinyloxy)oxazole derivatives have been synthesized by controlling the basicity of the reaction system. Key words oxazolone; oxazole; dehydrocondensation; cyclodehydration; aqueous solvent Oxazol-5(4H)-ones (henceforth referred to as oxazolones) are useful precursors for the synthesis of substituted heterocyclic compounds, 1) natural products, 2) and chiral amino acids. 3,4)In general, the preparation of oxazolones from amino acids is effected by two-step synthesis: N-acylation of the amino group followed by cyclodehydration involving the activation of the carboxy group. The N-acylation of amino acids can be carried out in an aqueous solvent, typically using Schotten-Baumann conditions, 5) while the cyclodehydration of the resulting N-acylamino acids to form oxazolones is performed under anhydrous conditions with dehydrating reagents, such as carbodiimides and acid anhydrides. Thus, these reactions must be performed in separate vessels. If the latter reaction occurs in an aqueous solvent, both reactions can be conducted in the same vessel using water-soluble amino acids as a starting compound. Therefore, the procedure for preparing oxazolones becomes simplified. In this study, we focused on 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) 6) as a dehydrocondensing reagent because the chemoselective activation of carboxy groups using DMT-MM efficiently proceeds even in an aqueous solvent. 7)We report here a one-pot method for the synthesis of oxazolones from amino acids. In this method, DMT-MM is utilized successfully for both the N-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids. 8,9) Results and DiscussionTo find the optimum reaction conditions for the one-pot method, we first examined each reaction separately using Lleucine (2a) as a model compound.10,11) After several attempts, we succeeded in finding the optimum reaction conditions for the first reaction. Benzoic acid (1) was treated with DMT-MM in the presence of N-methylmorpholine (NMM) in acetone-H 2 O (3 : 1) at room temperature for 15 min; then an aqueous solution of 2a and NaOH was added (Chart 1). As a result, N-benzoyl-L-leucine (3a) was obtained in a satisfactory yield (91%). The addition of NaOH as a base was found to be essential to complete the coupling reaction.The second reaction needs to follow the final conditions of the former reaction to achie...

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Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon

Cited by 220 publications

References 87 publications

Lewis Base Catalysis in Organic Synthesis

Lewis Base Catalysis in Organic Synthesis

Lewis‐Base‐Katalyse in der organischen Synthese

One-Pot Preparation of Oxazol-5(4<i>H</i>)-ones from Amino Acids in Aqueous Solvents

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