Enantioselective construction of C-B axially chiral alkenylborons by nickel-catalyzed radical relayed reductive
Weihua Qiu1, Rencai Tao1, Yong He1
1Key Laboratory of Molecule Synthesis and Function Discovery, Fujian Province University, College of Chemistry at Fuzhou University, Fuzhou, Fujian, 350108, China.
Abstract:
The catalytic asymmetric synthesis of axially chiral alkenes remains a daunting challenge due to the lower rotational barrier, especially for longer stereogenic axis (e.g. C-B axis). The asymmetric radical difunctionalization of alkynes represents an efficient strategy for these targets. Key to the success of such transformations lies in aryl-stabilized highly reactive alkenyl radical intermediates, however, it remains an elusive whether a boryl group could play a similar role. Here we report a nickel-catalyzed atroposelective radical relayed reductive coupling reaction of our designed ethynyl-azaborines with simple alkyl and aryl halides through a boron-stabilized vinyl radical intermediate. This transformation enables a straightforward access to the challenging axially chiral alkenylborons bearing a C-B axis in generally high enantioselectivity and excellent stereoselectivity.
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