A new class of bifunctional chiral phase transfer catalysts for highly enantioselective asymmetric epoxidation of α,β-unsaturated ketones at ambient temperature

• Quaternary ammonium bromide salt act as a highly efficient chiral multifunctional phase transfer catalyst.
• The asymmetric epoxidation reactions were carried out under lower concentration of oxidant and base at room temperature.
• The enantioselective epoxidation reactions are mild, fast, easy to perform, and proceeded with high yields (up to 98%) and ee’s (up to 99%).
• The formation of higher yield and ee's found in presence of CMPTCs due to the effective ion-pair contact between the R4N+ of the CMPTCs with enolate anion of the chalcone.
• The epoxide functional group is one of the most useful intermediates in organic synthesis and building blocks for the synthesis of biologically active compounds.

A new type of bis-quaternary ammonium bromide as chiral multifunctional phase transfer catalysts derived from readily available inexpensive cinchona alkaloids has been developed and evaluated for the enantioselective asymmetric epoxidation of various chalcones in the presence of lower concentrations of various oxidants, bases, solvents and ambient temperature conditions. Under optimized reaction conditions, highest chemical yields of up to 98% along with the excellent enantioselectivities of about 99% were obtained by using the cinchona based chiral multifunctional phase transfer catalysts.

Highly enantioselective epoxidation of various chalcones have been achieved under mild chiral multifunctional phase-transfer reaction conditions by the successful utilization of cinchona alkaloid based new chiral quaternary ammonium catalysts (10a and 10b). This asymmetric epoxidation process was found to be quite effective epoxides with very good yield (up to 98%) and ee’s (up to 99%).Figure optionsDownload high-quality image (133 K)Download as PowerPoint slide