Crown ether derived from D-glucose as an efficient phase-transfer catalyst for the enantioselective Michael addition of malonates to enones

A monoaza-15-crown-5 lariat ether derived from D-glucose (1) has been applied as chiral phase-transfer catalyst in the Michael addition of diethyl, dimethyl, diisopropyl and dibenzyl malonates to enones under mild conditions to afford the adducts in good to excellent enantioselectivities. In the reaction of diethyl malonate with substituted trans-chalcone, the adducts formed in enantioselectivities up to 89% ee. Among the reactions of substituted diethyl malonates, that of diethyl acetoxymalonate gave the best results (96% ee). The effect of the substituents of the chalcone was also investigated in reaction with diethyl acetoxymalonate. Among the chalcones substituted on the β side, the para-substituted compounds resulted in the highest enantioselectivities (88-97% ee). The substituents on the α-side of chalcone caused a decrease in the enantioselectivity, as compared to the unsubstituted case. The adducts having furyl or thiophenyl substituents were formed with >99% ee. The glucose-based catalyst also proved to be effective in the cases of diisopropyl and dibenzyl acetoxymalonates (including ee-s up to 99% ee). The reactions of diethyl acetoxymalonate with cyclic enones gave the corresponding Michael adducts in enantioselectivities up to 83%. The absolute configuration of one of the new Michael adducts was determined by CD spectroscopy