Transition-Metal-Free Synthesis of Borylated Thiophenes via Formal Thioboration

A simple, regiocontrolled, and transition-metal-free approach to access exclusively 3-borylated thiophene derivatives is reported. The commercially available B-chlorocatecholborane reagent (ClBcat) acts as a carbophilic Lewis acid to activate the alkyne in readily synthesized (Z)-organylthioenyne substrates. This boron-induced activation initiates the formal thioboration and subsequent sulfur dealkylation, leading to the formation of 3-borylated thiophenes in good yields. The resulting borylated thiophenes are isolable as boronic esters (Bpin) and boronamides (Bdan). These borylated products are amenable to diverse downstream functionalization reactions, i.e., C–C bond formation through cross-coupling, azidation, bromination, and C–H activation