Conformational analysis of 1,3,2-polymethyl-substituted dioxaborinanes

Abstract

Study of conformational isomerization of 4,4,6-trimethyl- and 4,4,6,6-tetramethyl-1,3,2-dioxaborinanes containing hydrogen, as well as methyl and vinyl groups at the boron atom, by means of nonempirical quantum-chemical calculation in HF/6–31G (d) and PBE/3z approximations, as well as by analysis of 1H NMR spectroscopic data was carried out. The molecules of the analogs with three methyl groups in the ring are in equilibrium between the half-chair and sofa conformers, the equilibrium is shifted almost completely toward the latter form. For the 4,4,6,6-tetramethyl-substituted cyclic boronic esters is characteristic the conformational equilibrium between energetically degenerated forms of either sofa, or half-chair.