The lithiumenolates of N-Boc protected pyroglutamic ethyl or tert-butyl esters react with electrophiles in good yield without epimerization of the chiral centre. With benzyl bromides the process is stereospecific, yielding exclusively the trans isomer. However, with other reactive electrophiles a 2:1 trans/cis diastereomeric mixture was obtained, regardless of the steric bulk of the ester group.
Synthesis of Enantiomerically Pure 4-Substituted Glutamic Acids and Prolines: General Aldol Reaction of Pyroglutamate Lactam Lithium Enolate Mediated by Et2O.cntdot.BF3
作者:Jesus Ezquerra、Concepcion Pedregal、Belen Yruretagoyena、Almudena Rubio、M. Carmen Carreno、Ana Escribano、Jose Luis Garcia Ruano