Regioselective Diversification of 2,1-Borazaronaphthalenes: Unlocking Isosteric Space via C-H Activation.

Methods for the regioselective C-H borylation and subsequent cross-coupling of the 2,1-borazaronaphthalene core are reported. Azaborines are dependent on B-N/C═C isosterism when employed in strategies for developing diverse heterocyclic scaffolds. Although 2,1-borazaronaphthalene is closely related to naphthalene in terms of structure, the argument is made that the former has electronic similarities to indole. Based on that premise, iridium-mediated C-H activation has enabled facile installation of a versatile, nucleophilic coupling handle at a previously inaccessible site of 2,1-borazaronaphthalenes. A variety of substituted 2,1-borazaronaphthalene cores can be successfully borylated and further cross-coupled in a facile manner to yield diverse C(8)-substituted 2,1-borazaronaphthalenes.