Ligand-Controlled Enantioselective Copper-Catalyzed Hydroboration and Ring-Opening Dihydroboration of Arylidenecyclobutanes
Wenrui Zheng, Yuhan Cao, Boon Beng Tan, Yifan Wang, Shaozhong Ge, Yixin Lü
Abstract
Arylidenecyclobutanes are readily accessible and versatile reagents in synthetic chemistry due to the multifaceted reactivity exhibited by their alkene and strained cyclobutane moieties. However, metal-catalyzed enantioselective functionalization of arylidenecyclobutanes, particularly the controllable ring-retaining and ring-opening reactions, is rarely explored. Considering the versatile synthetic utility of enantioenriched organoboronate compounds, herein we report ligand-controlled enantioselective copper-catalyzed ring-retaining hydroboration and ring-opening dihydroboration reactions of arylidenecyclobutanes that afford chiral α -cyclobutyl benzylboronate and 1,5-diboronate compounds with high enantioselectivity when ( S )-DTBM-Segphos and ( S, S )-Ph-BPE are employed, respectively. Mechanistic studies reveal that the ring-opening process of arylidenecyclobutanes via β-C elimination is significantly slower than that of arylidenecyclopropanes in the presence of CuOAc and ( S, S )-Ph-BPE. The synthetic utility of these two enantioselective protocols is further demonstrated through conducting various stereospecific and site-selective transformations of the enantioenriched organoboron products, including concise synthesis of bioactive molecules.