A FMO-controlled reaction path in the benzil-benzilic acid rearrangement.
Reaction paths for the title rearrangement along with its methyl analogue were investigated by density functional theory calculations. The reaction model is R-CO-CO-R + OH(-)(H2O)4 --> R2C(OH)-COO- + (H2O)4 (R = Me and Ph), where the water tetramer is employed both for solvation to OH- and for the proton relay along hydrogen bonds. The reaction is composed of OH- addition, C-C rotation, carbanion [1,2] migration, and proton relay toward the product anions. The rate-determining step was calculated to be the carbanion migration. Apparently, carbanion [1,2] migration is unlikely relative to the carbonium ion one. However, LUMOs of the 1,2-diketones have large and nodeless lobes at the reaction center, the C1-C2 bond. The specific LUMO character is reflected both in the [2+1]-like one-center nucleophilic addition and in the carbanion [1,2] shift. The proton relay involved in the isomerization from the oxo intermediate to the carboxylate was calculated to take place via the water tetramer.
Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528, Japan. yamabes@nara-edu.ac.jp
Shinichi
S
Yamabe
Noriko
N
Tsuchida
Shoko
S
Yamazaki