Catalyst-Free Synthesis of Borylated Lactones from Esters via Electrophilic Oxyboration

A catalyst-free oxyboration reaction of alkynes is developed. The resulting borylated isocoumarins and 2-pyrones are isolated as boronic acids, pinacolboronate esters, or potassium organotrifluoroborate salts, providing a variety of bench-stable organoboron building blocks for downstream functionalization. This method has functional group compatibility, is scalable, and proceeds with readily available materials: B-chlorocatecholborane and methyl esters. Mechanistic studies indicate that the B-chlorocatecholborane acts as a carbophilic Lewis acid toward the alkyne, providing a mechanistically distinct pathway for oxyboration that avoids B-O sigma bond formation and enables this catalyst-free route.