Stereoselective Synthesis of Dihydrofuranoindoles via the Friedel–Crafts Alkylation/Annulation Cascade Process

A stereoselective
annulation protocol was developed to construct
dihydrofuranoindoles from readily available starting materials. In
the presence of a bifunctional squaramide, the Friedel–Crafts
alkylation/annulation cascade process occurred smoothly to provide
dihydrofuranoindoles in 26–95% isolated yields exclusively
as trans-diastereomers (38–99% ee). This catalytic
protocol was compatible with a range of structurally distinct hydroxyindoles
bearing the hydroxyl group at different positions, providing four
kinds of dihydrofuranoindoles. Moreover, gram-scale synthesis and
further synthetic manipulation of the product were also demonstrated.