Palladium- and Ruthenium-Catalyzed Intramolecular Carbene CAr−H Functionalization of γ-Amino-α-diazoesters for the Synthesis of Tetrahydroquinolines |
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Authors: | Prof Dr Daniel Solé Arianna Amenta Prof Dr M-Lluïsa Bennasar Prof Dr Israel Fernández |
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Institution: | 1. Laboratori de Química Orgànica, Facultat de Farmàcia i Ciències de l'Alimentació, Universitat de Barcelona, Av. Joan XXIII 27–31, 08028 Barcelona, Spain;2. Departamento de Química Orgánica I and Centro de Innovación en, Química Avanzada (ORFEO-CINQA), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain |
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Abstract: | A synthetic method to prepare tetrahydroquinoline-4-carboxylic acid esters has been developed through the transition-metal-catalyzed intramolecular aromatic C−H functionalization of α-diazoesters. Both {Pd(IMes)(NQ)}2] (IMes=1,3-dimesitylimidazol-2-ylidene, NQ=1,4-naphthoquinone) and the first-generation Grubbs catalyst proved effective for this purpose. The ruthenium catalyst was found to be the most versatile, although in a few cases the palladium complex afforded better yields or selectivities. According to DFT calculations, Pd0- and RuII-catalyzed sp2-CAr−H functionalization proceeds through different reaction mechanisms. Thus, the Pd0-catalyzed reaction involves a Pd-mediated 1,6-H migration from the sp2-CAr−H bond to the carbene carbon atom, followed by a reductive elimination process. In contrast, electrophilic addition of the ruthenacarbene intermediate to the aromatic ring and subsequent 1,2-proton migration are operative in the Grubbs catalyst promoted reaction. |
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Keywords: | carbenes density functional calculations homogeneous catalysis palladium ruthenium |
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