Understanding the regioselectivity and molecular mechanism in the synthesis of isoxazoles containing pentafluorosulfanyl substitution via a [3+2] cycloaddition reaction: A DFT study

摘要: Abstract A theoretical study was performed on the [3+2] cycloaddition (32CA) reaction of benzonitrile oxide, BNO 4, toward phenyl SF5-acetylene, PAC 5, in presence tetrahydrofuran (THF) at DFT-B3LYP/6-31G* level. Calculated relative Gibbs free energies indicate that studied 32CA takes place via a complete C1 C4 regioselective channel passing through TS1 affording unique formal cycloadduct CA1 observed experimentally. While based calculated Parr functions interacting sites reagents this should proceed energetically unfavorable C5 TS2, natural steric analysis evidently showed destabilizing repulsion effects, rather than electronic ones, are responsible for fashion provided by considered reaction. An ELF topological bonding changes along supports non-concerted two-stage one-step molecular mechanism which formation second O3 single bond when first one is almost complete.