Metal‐Catalyzed Cyclization of β‐ and γ‐Allenols Derived from D‐Glyceraldehyde—Synthesis of Enantiopure Dihydropyrans and Tetrahydrooxepines: An Experimental and Theoretical Study |
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Authors: | Benito Alcaide Prof Dr Pedro Almendros Dr Teresa Martínez del Campo Dr Elena Soriano Dr José L Marco‐Contelles Prof Dr |
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Institution: | 1. Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense de Madrid, 28040 Madrid (Spain), Fax: (+34)?91‐3944103;2. Instituto de Química Orgánica General, Consejo Superior de Investigaciones Científicas, CSIC, Juan de la Cierva 3, 28006 Madrid (Spain), Fax: (+34)?91‐5644853 |
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Abstract: | Regiocontrolled metal‐catalyzed preparations of enantiopure dihydropyrans and tetrahydrooxepines have been synthesized starting from β‐ and γ‐allenols derived from D ‐glyceraldehyde. The PdII‐catalyzed cyclizative coupling reactions of β‐allenols 1 a and 1 b with allyl bromide effectively afforded enantiopure tetrafunctionalized dihydropyrans through a 6‐endo oxycyclization protocol, whereas the gold‐, platinum‐, and palladium‐mediated heterocyclization of γ‐allenol 2 furnished tetrahydrooxepines 13 – 16 through regioselective 7‐endo‐trig oxycyclization reactions. Moreover, density functional calculations were performed to predict the regioselectivity of the γ‐allenol cycloetherification to tetrahydrooxepines on the basis of both the tether nature and characteristics of the metals, and to gain an insight into the mechanism of the oxycyclization reactions. |
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Keywords: | allenes cyclization gold palladium platinum reaction mechanisms |
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