Striking alkenol versus allenol reactivity: metal-catalyzed chemodifferentiating oxycyclization of enallenols

An efficient chemodivergent metal-controlled methodology for the generation of different highly functionalized oxygen heterocycles from common enallenol substrates has been developed. Chemoselectivity control in the O-C functionalization of an enallenol can be achieved through the choice of catalyst: AuCl(3), PdCl(2), and [PtCl(2)(CH(2)=CH(2))](2) exclusively afford dihydrofurans through selective activation of the allenol moiety, whereas FeCl(3) solely gives tetrahydrofurans or tetrahydropyrans through selective activation of the alkenol moiety. We have also shown that a combination of metal-mediated hydroalkoxylation and allenic aminocyclization reactions can lead to a useful preparation of the tetrahydrofuro[3,2-b]piperidine core of the antimalarial alkaloid isofebrifugine. These divergent heterocyclization reactions have been developed experimentally and additionally, their mechanisms have been investigated by a theoretical study.