Cobalt-Catalyzed Asymmetric Remote Borylation of Alkyl Halides.

Enantioselective functionalization of racemic alkyl halides is an efficient strategy to assemble complex chiral molecules, but remains one of the biggest challenges in organic chemistry. The distant and selective activation of unreactive C-H bonds in alkyl halides has received growing interest as it enables rapid generation of molecular complexity from simple building blocks. Here, we reported a cobalt-catalyzed remote borylation of alkyl (pseudo)halides (alkyl-X, X=I, Br, Cl, OTs) with pinacolborane (HBpin) and presented a robust approach for the generation of valuable chiral secondary organoboronates from racemic alkyl halides. This migration borylation reaction is compatible with primary, secondary, and tertiary bromides, offering direct access to a broad range of alkylboronates. The extension of this catalytic system to the borylation of aryl halides was also demonstrated. Preliminary mechanistic studies revealed that this remote borylation involved a radical reaction pathway.

Transition-Metal-Free Cross-Coupling by Using Tertiary Benzylic Organoboronates.

The transition-metal-free cross-coupling of alkyl or aryl electrophiles by using tertiary benzylic organoboronates is reported. This reaction involves the generation of tertiary alkyl anions from organoboronates in the presence of an alkoxide base and then their substitution reactions. This protocol allows the simple and efficient construction of quaternary carbon centers.

Photoinduced Radical Borylation of Alkyl Bromides Catalyzed by 4-Phenylpyridine.

Utilizing pyridine catalysis, we developed a visible-light-induced transition-metal-free radical borylation reaction of unactivated alkyl bromides that features a broad substrate scope and mild reaction conditions. Mechanistic studies revealed a novel nucleophilic substitution/photoinduced radical formation pathway, which could be utilized to trigger a variety of radical processes.