Base‐Modulated 1,3‐Regio‐ and Stereoselective Carboboration of Cyclohexenes

Abstract

While chain‐walking stimulates wide interest in both polymerization and organic synthesis, site‐ and stereoselective control of chain‐walking on rings is still a challenging task in the realm of organometallic catalysis. Inspired by a controllable chain‐walking on cyclohexane rings in olefin polymerization, we have developed a set of chain‐walking carboborations of cyclohexenes based on nickel catalysis. Different from the 1,4‐trans‐selectivity disclosed in polymer science, a high level of 1,3‐regio‐ and cis‐stereoselectivity is obtained in our reactions. Mechanistically, we discovery that the base affects the reduction ability of B2pin2 and different bases lead to different catalytic cycles and different regioselective products (1,2‐ Vs 1,3‐addition). This study provides a concise and modular method for the synthesis of 1,3‐disubstituted cyclohexylboron compounds. The incorporation of a readily modifiable boronate group greatly enhances the value of this method, the synthetic potential of which was highlighted by the synthesis of a series of high‐valued commercial chemicals and pharmaceutically interesting molecules.

Nickel Chain-Walking Catalysis: A Journey to Migratory Carboboration of Alkenes

“…Building on Takeuch's palladium-catalyzed isomerization polymerization of alkenylcyclohexanes, 55 we ventured into migratory carboboration reactions of cyclohexene (Figure 7C). 4 However, contrary to Takeuchi's work that yielded polymers containing trans-cyclohexane-1,4-diyl monomer units, the nickel-catalyzed carboboration reaction produced 1,3-regioselective products with significant cis-stereoselectivity. The reaction accommodates diverse coupling partners like benzyl halides, primary and secondary alkyl bromides, and aryl bromides.…”

“…Therefore, migratory difunctionalization of cyclohexene can potentially yield both 1,3- and 1,4-addition products. Building on Takeuch’s palladium-catalyzed isomerization polymerization of alkenylcyclohexanes, we ventured into migratory carboboration reactions of cyclohexene (Figure C) . However, contrary to Takeuchi’s work that yielded polymers containing trans -cyclohexane-1,4-diyl monomer units, the nickel-catalyzed carboboration reaction produced 1,3-regioselective products with significant cis -stereoselectivity.…”