Metal-Catalyzed Cyclization of b- and g-Allenols Derived from d-Glyceraldehyde—Synthesis of Enantiopure Dihydropyrans and Tetrahydrooxepines: An Experimental and Theoretical Study

摘要

Regiocontrolled metal-catalyzed preparations of enantiopure ihydropyrans and tetrahydrooxepines have been synthesized starting from b- and g-allenols derived from d-glyceraldehyde. The PdII-catalyzed cyclizative coupling reactions of b-allenols 1a and 1b with allyl bromide effectively afforded enantiopure tetrafunctionalized dihydropyrans through a 6-endo oxycyclization protocol, whereas the gold-,platinum-, and palladium-mediated heterocyclization of g-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 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.