The role of hydrogen bonds in Baeyer-Villiger reactions

Various Baeyer-Villiger (B-V) oxidation reactions were examined by density functional theory calculations. Proton movements in transition states (TSs) of the two key steps, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) and the migration-cleavage of O-O (TS3), were discussed. A new TS of a hydrogen-bond rearrangement in the Criegee intermediate (TS2) was found. The hydrogen-bond directionality requires a trimer of the peroxyacid molecules at the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1). At the migration-cleavage of O-O TS (TS3), also three peroxyacid molecules are needed. Elementary processes of the B-V reaction were determined by the use of the (acetone and (H-CO-OOH)n, n=3) system. The geometries of the nucleophilic addition of a peroxyacid molecule to a ketone TS (TS1) and the migration-cleavage of O-O TS (TS3) in the trimer (n=3) participating are nearly insensitive to the substituent on the peroxyacid. The directionality is satisfied in those geometries. The migration-cleavage of O-O TS (TS3) was found to be rate-determining in reactions, [Me2C=O+(H-CO-OOH)3], [Me2C=O+(F3C-CO-OOH)3], and [Me2C=O+(MCPBA)3]. In contrast, the nucleophilic addition of a peroxyacid molecule to a ketone (TS1) is rate-determining in the reaction, [Ph(Me)C=O+(H-CO-OOH)3].