A novel synthetic method for chiral α,α-dialkylmalonate via phase-transfer catalytic alkylation

Abstract

Chiral α-malonates have popularly been utilized as the construction of chiral α-quaternary carbon centers of biologically active pharmaceuticals and natural products. In our research, 5 kinds of malonate substrates were firstly screened by asymmetric phase-transfer catalytic α-benzylation. 2,2-diphenylethyl malonate was then chosen as a final substrate and applied for further optimization of reaction conditions. High enantioselectivity (up to 99% ee) was achieved via enantioselective phase-transfer catalytic reaction using 50% aqueous potassium hydroxide as base and toluene as solvent under -40℃. Furthermore, the scope of electrophiles, such as allyl bromide, 4-methylbenzyl bromide and 3-methoxybenzyl bromide, in the optimized enantioselective PTC reaction was determined. In addition, the selective hydrolysis, the objective of designing the new malonate substrate, in alkali basic and TFA acidic conditions was confirmed. In conclusion, we reported an attractive synthetic method for establishing an α,α-quaternary malonate carbon center by enantioselective phase-transfer catalysis to achieve excellent chemical yields and optical yields.