Enantioselective Synthesis of Pyroglutamic Acid Esters from Glycinate via Carbonyl Catalysis

Abstract

Direct a‐functionalization of NH 2 ‐free glycinates with relatively weak electrophiles such as α,β‐unsaturated esters still remains a big challenge in organic synthesis. With chiral pyridoxal 5d as a carbonyl catalyst, direct asymmetric conjugated addition at the α‐C of glycinate 1a with α,β‐unsaturated esters 2 has been successfully realized, to produce various chiral p yroglutamic acid esters 4 in 14~96% yields with 81~97% ee’s after in situ lactamization. The trans ‐ and cis ‐diastereomers can be obtained at the same time by chromatography and both of them can be easily converted into chiral 4‐substituted pyrrolidin‐2‐ones such as Alzheimer’s drug Rolipram ( 11 ) with the same absolute configuration via tert ‐butyl group removal and subsequent Barton decarboxylation.