Triborane (B3H7)-Mediated Regioselective Substitution Reactions of Pyridine Derivatives

Abstract

The interplay between borane and the Lewis base exists in their adducts. However, the studies on these adducts so far mainly focus on the different reactions of the B-H bonds and little attention to the influence of borane on the chemistry of the Lewis base, except for BF3 and BAr3. Herein, we have synthesized novel borane adducts with pyridine derivatives, Py∙B3H7, in which the coordination of B3H7 efficiently achieved the intra-molecular charge transfer. The strong B-N bond in these adducts resulted in the formation of stable dearomatic intermediates of pyridine derivatives, confirmed by 1H and 11B NMR spectroscopy, from which different reactions have transpired to realize the C(sp3)-H and C(sp2)-H functionalization under mild conditions. The B3H7 pyridine derivatives are stable and do not dissociate or decompose during the reaction process. Such high stability of the B−N bond makes this method a good option for boron-containing drugs, potentially used in boron neutron capture therapy (BNCT).