Orthogonal C–B Bond Transformation as an Approach for Versatile Synthesis of End-Functionalized Polymers

Conventionally inaccessible end-functionalized vinyl polymers were synthesized via orthogonal side-chain replacement for terminal and repeating units of poly­(alkenyl boronate)­s. A terminal-defined polymer of isopropenyl boronic acid pinacol ester (IPBpin) was synthesized via RAFT polymerization, and subsequent cobalt (Co)-catalyzed end olefination afforded the polymer carrying the C­(sp²)–B bond at the terminal and the C­(sp³)–B bond in repeating units. Herein, the terminal C­(sp²)–B bond was selectively transformable via palladium (Pd)-catalyzed Suzuki-Miyaura cross coupling, and subsequent transformation of the repeating C­(sp³)–B unit gave the poly­(α-methyl vinyl alcohol) [poly­(MVA)] bearing various functional groups at the terminal. The boron-based stepwise polymer reaction thus overcame the synthetic difficulty of the end-functionalized poly­(MVA), which is ascribed to the poor polymerization ability of the corresponding acetate monomer, i.e., isopropenyl acetate.