β-Selective C( sp 3)-H functionalization of alkyl boronates using photoredox catalysis.

Abstract

Alkyl boronates are a versatile class of organic molecules that have transformed chemical synthesis and had a broad impact in drug discovery, agrochemistry and materials research. For over 50 years, the conventional use of alkyl boronates has been the direct reaction of the C-B bond for the formation of C-C, C-N, C-O and C-X bonds. Here we report the use of alkyl boronates as directing groups to perform site-selective C(sp3)-H functionalization at the distal site. This methodology involves classic Lewis pair chemistry; it uses an alkyl-BF2, generated in situ from alkyl trifluoroborate salts, as a Lewis acid and 2-haloheteroarene as a Lewis base. Under mild photoredox reaction conditions, we are able to site-selectively functionalize the β-position of a wide range of alkyl trifluoroborate salts with the corresponding heteroarene through a cascade sequence of single-electron reduction, hydrogen atom transfer and intramolecular heteroaryl migration. This transformation effectively upgrades alkyl boron compounds into structurally complex heteroarene-containing building blocks.

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