Multifunctionalization of N‐Heterocyclic Carbene Boranes by a Single Metal‐free Photocatalyst

Selective access to densely functionalized boranes, with identical or distinct functional groups at the boron center, has great potentials in materials science, organic synthesis and drug discovery. However, assembling multifunctional boranes was heavily dependent on hydrogen‐atom‐transfer (HAT) at high temperatures, hazardous radical initiators, metal photocatalysts and HAT reagents, respectively. Simultaneously, competitive side reactions such as polymerizations and regioisomers formation remain highly challenging. Herein, a programmable multifunctionalization of N‐heterocyclic carbene (NHC) boranes is developed for the first time powered by a single, metal‐free photocatalyst, in which boryl radicals from sequential substituted boranes are generated instead of polymerizations. This robust and versatile catalytic system leads to an extremely broad variety of boranes incorporated with diverse alkyl or alkenyl groups in high chemo‐ and regioselectivities.