Regioselective Syntheses of Bis(indazolyl)methane Isomers: Controlling Kinetics and Thermodynamics via Tunable Non-Innocent Amines

The selective synthesis
of regioisomers from ambident N-heterocycles
remains a challenge in organic chemistry. We report a general and
modular method for the regioselective syntheses of bis(indazolyl)methane
isomers, in which the outcome is controlled by the nature of the base.
Specifically, we employed structurally diverse amines as noninnocent
bases, whose steric and electronic propertiesparticularly
their pKaH and ability to act as methylene
carriers or activatorsplay a decisive role in directing product
distribution. By fine-tuning the amine structure, we achieved selective
access to symmetrical and unsymmetrical isomers under mild, one-step
conditions, without intermediate isolation. The use of amines over
conventional inorganic bases was essential to enable both chemo- and
regioselective control, while minimizing overactivation or competing
pathways. Experimental findings were supported by DFT calculations
that rationalize the observed selectivity through differential activation
energies and intermediate stabilities. The methodology accommodates
both classical methylenating agents (e.g., CH2Br2) and in situ generated ammonium-based donors. All compounds were
fully characterized, and key products were confirmed by single-crystal
X-ray diffraction (SCXRD). This strategy highlights the utility of
noninnocent amines as tunable reagents for regioselective transformations
of ambident nucleophiles, with broad potential applications in ligand
design, supramolecular chemistry, and heterocyclic synthesis.