Enantioselective Synthesis of Chiral α‑Thio-Quaternary Stereogenic Centers via Phase-Transfer-Catalyzed α‑Alkylation of α‑Acylthiomalonates

An
efficient synthetic method for establishing chiral α-thio-α-quaternary
stereogenic center was successfully developed. The enantioselective
α-alkylation of α-acylthiomalonates under phase-transfer
catalytic conditions [50% aq. KOH, toluene, −20 °C, and
(S,S)-3,4,5-trifluorophenyl-NAS
bromide] provided the corresponding α-acylthio-α-alkylmalonates
in high chemical yields (up to 99%) and high optical yields (up to
98% ee).