Activation of olefins via asymmetric Bronsted acid catalysis

The activation of olefins for asymmetric chemical synthesis traditionally relies on transition metal catalysts. In contrast, biological enzymes with Bronsted acidic sites of appropriate strength can protonate olefins and thereby generate carbocations that ultimately react to form natural products. Although chemists have recently designed chiral Bronsted acid catalysts to activate imines and carbonyl compounds, mimicking these enzymes to protonate simple olefins that then engage in asymmetric catalytic reactions has remained a substantial synthetic challenge. Here, we show that a class of confined and strong chiral Bronsted acids enables the catalytic asymmetric intramolecular hydroalkoxylation of unbiased olefins. The methodology gives rapid access to biologically active 1,1-disubstituted tetrahydrofurans, including (-)-Boivinianin A.