Metal-catalyzed cyclization of beta- and gamma-allenols derived from D-glyceraldehyde--synthesis of enantiopure dihydropyrans and tetrahydrooxepines: an experimental and theoretical study.
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.
Alcaide
Benito
B
Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense de Madrid, 28040 Madrid, Spain. alcaideb@quim.ucm.es
Almendros
Pedro
P
Martínez del Campo
Teresa
T
Soriano
Elena
E
Marco-Contelles
José L
JL