The controlled-potential electrolysis of racemic ethyl 3-bromo-2-methoxy-2-phenylpropionate was carried out at -1.8V vs. SCE in N,N-dimethylformamide, as mediated by a simple hydrophobic vitamin B12, [Cob(II)7C3ester]ClO4, and a strapped hydrophobic vitamin B12, [Cob(II)(c,10-PDA)6C3ester]ClO4, to afford ethyl 2-methoxy-2-phenylpropionate and ethyl 2-methoxy-3-phenylpropionate in the dark. The simple hydrophobic vitamin B12 acted to afford ethyl (S)-2-methoxy-2-phenylpropionate, the hydrogen-substituted product, in 55% e.e., while the strapped hydrophobic vitamin B12 was in favor of formation of the corresponding R enantiomer in 26% e.e. Since the reaction proceeds via formation of an intermediate in which the ethyl 2-methoxy-2-phenylpropionate moiety is bound to the hydrophobic vitamin B12, the chiral microenvironment provided by the peripheral groups placed around the corrin framework is responsible for the enantioselective formation of the alkylated hydrophobic vitamin B12. The enantioselective coordination of the substrate species was rationalized by means of molecular mechanics and dynamics computations as well as by Monte Carlo conformational search; the simple hydrophobic vitamin B12 with the S substrate is lower in energy than the complex with the R substrate by l.8 kJ mol-1, while the strapped hydrophobic vitamin B12 with the R substrate is lower than the identical complex with the S substrate by 2.0 kJ mol-1.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry