Stereoselective reactions of lithium enolates derived from N-BOC protected pyroglutamic estersBy: Ezquerra, Jesus; Pedregal, Concepcion; Rubio, Almudena; Yruretagoyena, Belen; Escribano, Ana; Sanchez-Ferrando, FranciscoTetrahedron (1993), 49(38), 8665-78 | Language: English, Database: CAplusThe lithium enolates of protected pyroglutamate esters I (R = H, R1 = Et, CMe3; Boc = Me3CO2C) react with electrophiles in good yield without epimerization of the chiral center. With benzyl bromides the process is stereospecific, yielding exclusively trans isomers I (R = PhCH2, 4-MeC6H4CH2, 4-CF3C6H4CH2, 4-BrC6H4CH2, 4-NCC6H4CH2, 2-naphthylmethyl). However, with other reactive electrophiles a 2:1 trans/cis diastereomeric mixture was obtained, regardless of the steric bulk of the ester group.