Ligand-Controlled Enantioselective Copper-Catalyzed Hydroboration and Ring-Opening Dihydroboration of Arylidenecyclobutanes.

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.