Synthesis of α-substituted cyclic boronates via titanium-catalyzed cyclization of vinyl boronates with dihaloalkanes.

Cyclic boronates are versatile synthons for organic synthesis and for introducing ring systems into bioactive molecules. Existing synthetic methods have narrow substrate scope and the synthesis of α-substituted cyclic boronates is still elusive. Furthermore, no general method for synthesizing cyclic boronates with different ring sizes and hetero atom containing rings is available. Herein, we present a new and general synthetic method for synthesizing α-substituted cyclic boronates. Our approach has the advantage of using earth-abundant Ti as the catalyst and readily available dihaloalkanes, such as dichloromethane, as the reactant. Cyclic boronates that are otherwise difficult to access, such as α-substituted cyclic boronates with three-, four-, five-, and six-membered rings, heteroatom-containing rings, and cyclic boronates with spiro rings, are readily obtained.