title: Metal-catalyzed cyclization of beta- and gamma-allenols derived from D-glyceraldehyde--synthesis of enantiopure dihydropyrans and tetrahydrooxepines: an experimental and theoretical study.
abstract: Regiocontrolled metal-catalyzed preparations of enantiopure dihydropyrans and tetrahydrooxepines have been synthesized starting from beta- and gamma-allenols derived from D-glyceraldehyde. The Pd(II)-catalyzed cyclizative coupling reactions of beta-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 gamma-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 gamma-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.
authors.affiliation: Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense de Madrid, 28040 Madrid, Spain. alcaideb@quim.ucm.es
authors.forename: Benito
authors.initials: B
authors.lastname: Alcaide
authors.forename: Pedro
authors.initials: P
authors.lastname: Almendros
authors.forename: Teresa
authors.initials: T
authors.lastname: Martínez del Campo
authors.forename: Elena
authors.initials: E
authors.lastname: Soriano
authors.forename: José L
authors.initials: JL
authors.lastname: Marco-Contelles