Triborane (BH)-mediated regioselective substitution reactions of pyridine derivatives.

There exists an interplay between borane and a Lewis base in their adducts. However, studies on these adducts so far have mainly focused on the different reactions of B-H bonds with limited attention given to the influence of borane on the chemistry of the Lewis base, except for BF and BAr. Herein, we have synthesized novel borane adducts with pyridine derivatives, Py·BH, in which the coordination of BH 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 H and B NMR spectroscopy, from which different reactions have transpired to realize C(sp)-H and C(sp)-H functionalization under mild conditions. The BH pyridine derivatives are stable and do not dissociate or decompose during the reaction process. The high stability of the B-N bond makes this method a good option for boron-containing drugs with potential for use in boron neutron capture therapy (BNCT).