Regio- and Diastereoselective Synthesis of Cyclohexadienylborons via an Intermolecular Diels–Alder Reaction of Alkenyl MIDA Boronates with 2-Pyrones

An efficient synthesis of highly functionalized cyclohexadienylborons via an inverse electron-demand Diels–Alder reaction/CO₂ extrusion of alkenyl MIDA boronates with 2-pyrones is outlined. By controlling the reaction temperature, the corresponding C(sp³)-rich bicyclolactones could also be readily formed. The exo-selective reactions feature good functional-group tolerance, broad substrate scope, and excellent regio- and diastereoselectivity. Oxidation of the cyclohexadienylborons in a one-pot procedure led to the construction of aromatic boronates bearing valuable functional groups. Synthetic transformations of the C?B bond were demonstrated.