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 σ bond formation and enables this catalyst-free route.