Intramolecular C=O···B Interactions in o-Boron Substituted Benzaldehyde, Acetophenone, and Benzophenone

Abstract The title carbonyl compounds bearing a 4,4-diphenyl-1,3,2-dioxaborolan-2-yl group at the ortho position were prepared to compare the Lewis basicity of carbonyl-oxygen atoms. In the benzoyl and formyl compounds, the intramolecular C=O···B interactions are so weak that no significant changes were observed in the 13C and 11B NMR and IR spectra compared with the reference compounds. For the acetyl compound, the C=O stretching absorption was shifted to lower wavenumber by 18 cm−1 in the IR spectrum because of the coordination. The interaction energy could be estimated to be ca. 27 kJ mol−1 by the variable temperature 1H NMR measurement. These substituent effects are discussed from the viewpoints of Lewis basicity and the conformational stability of the carbonyl moieties with the assistance of the DFT calculations.