Tunable Lewis Basicity and Nucleophilicity of Water against α,α-Dihalo-β-acetoxyketones for the Selective Synthesis of α-Haloenones and 1,2-Diketones.

The discovery and systematic study of tunable yet competitive nucleophilicity and Lewis basicity of water against novel building blocks α,α-dihalo-β-acetoxyketones (possessing a tertiary acetate) have been reported. This distinct reactivity resulted in the formation of two competitive and different products 1,2-diketones and α-haloenones from a common intermediate α,α-dihalo-β-acetoxyketones through the nucleophilicity and Lewis basicity of water, respectively. A systematic study to understand the effect of temperature and amount of water on the product distribution revealed that a lower temperature in combination with a higher amount of water shows a high preference for 1,2-diketones over α-haloenones. Measuring the dielectric constant (permittivity, ε) of various reaction media at various temperatures and a correlation with the experimental observations suggested that the reaction media with a higher dielectric constant exhibit the nucleophilic character and hence show a preference for 1,2-diketones over α-haloenones.