91PORN

As organoboranes are valuable reagents in organic synthesis due to their versatility in functionalization, the demand for stereochemically well-defined organoboronates is increasing. In general, the creation of simple secondary alkylboron compounds with high enantiocontrol presents a greater challenge than the production of boron compounds with a biasing or directing substituent. Recent approaches to the synthesis of organoboron compounds by copper-catalyzed allylic substitution is the installation of the C−B bond using a diboron or 1,1-diborylalkanes as the organometallic component. All of these methods discard one B moiety from the diboron starting materials during activation and require the use of stereochemically well-defined prochiral allylic electrophiles. Herein, Prof. YUN reports a highly enantioselective synthesis of homoallylic alkylboron compounds starting from easily preparable alkylboron compounds, by tandem addition of B-α-chiral organocopper species to allyl phosphates. The keys to successful transformation are (1) highly regio- and enantioselective hydrocupration to borylalkenes and (2) subsequent asymmetric C−C bond formation with high efficiency. They believe this protocol provides easy access to chiral secondary homoallylic alkylboron compounds and efforts to expand the use of B-α-chiral organocopper species in catalytic bond formations are currently underway.