Transition-metal-free reactions of boronic acids: 1,3-stereochemical induction in the substrate-controlled conjugate addition.

The substrate-controlled 1,3-stereoselective conjugate addition of boronic acids and potassium trifluoroborates under metal-free conditions has been developed. This reaction affords bicyclic acetals, which have been used as key intermediates in the stereodivergent synthesis of polysubstituted tetrahydropyrans.