Switching of (N,O)- to (C,N)-Chelation in π‑Expanded Boron Quinolates

We report an intramolecular nucleophilic arylative dearomatization of diarylboron quinolates, leading to the formation of respective products where the boron atom is chelated by the 1,2-dihydroquinolate moiety. Kinetics and thermodynamics of this reaction were analyzed by density functional theory (DFT) calculations. Subsequent oxidation of obtained complexes with MnO2 in refluxing CHCl3 presumably gives rise to unstable, highly strained, rearomatized intermediates, which immediately undergo ethanolysis in situ, giving rise to EtO-substituted arylboron (C,N)-chelate complexes bearing a free OH group at the quinoline moiety. Treatment of these compounds with BF3·Et2O afforded two crystallographically authenticated diboron systems, where the 2-(8-oxidoquinolin-2-yl)aryl moiety is bound to the B(μ–OH)BF2 fragment.