Domino Synthesis of Bicyclic 3,5-Anhydro Furanose Mimics Using a Binary Al(III) Complex/Halide Catalyst

Structurally diverse heterobicyclic diethers can be conveniently accessed in good yields through a catalytic domino process that is controlled by a versatile binary catalyst comprising an Al(III) aminotriphenolate complex and a bromide salt. These bicycles, representing nonnatural, 3,5-anhydro furanose mimics, are derived from bis-epoxy substrates through a double cyclization pathway that is initiated by the activation of the free alcohol in the precursor compounds. Various mechanistic control experiments, X-ray analyses, and computational investigations allowed us to rationalize the intricacies of this multistep process and the role of each catalyst component while revealing a clear preference for a sequence that starts with oxetane ring formation followed by an annulation step forming a fused and substituted tetrahydrofuran.