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.
A facile and highly efficient method for one-pot four-component synthesis of triazolyl methoxy phenylquinazolines is described. A mixture of aromatic propargylated aldehydes, different azides, 2-aminobenzophenone derivatives, and ammonium acetate were condensed in the presence of catalytic amounts of acidic ionic liquid, 1-methylimidazolium trifluoroacetate, ([Hmim]TFA), and Cu(OAc)(2)/sodium ascorbate to afford the corresponding products in excellent yields. This methodology is highly efficient for structurally diverse azides.
An
approach to access azaborininones (carbonyl-containing, boron-based
heterocyclic scaffolds) using simple reagents and conditions from
both organotrifluoroborates and boronic acids is described.
An inexpensive, common reagent, SiO2, was found to serve
as both a fluorophile and desiccant to facilitate the annulation process
across three different azaborininone platforms. Computational analysis
of some of the cores synthesized in this study was undertaken to compare
the azaborininones with the analogous carbon-based heterocyclic systems.
Computationally derived pKa values, NICS
aromaticity calculations, and electrostatic potential surfaces revealed
a unique isoelectronic/isostructural relationship between these azaborines
and their carbon isosteres that changed based on boron connectivity.
Correlation to experimentally derived data supports the computational
findings.
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