Enantioselektive α‐Alkylierung von Asparagin‐ und Glutaminsäure über die Dilithium‐enolatocarboxylate von 2‐[3‐Benzoyl‐2‐(<i>tert</i>‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]essigsäure und 3‐[3‐Benzoyl‐2‐(<i>tert</i>‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]propionsäure

Abstract

Overall Enantioselective α‐Alkylation of Aspartic and Glutamic Acid through Dilithium Enolatocarboxylates of 2‐ [3‐Benzoyl‐2‐( tert ‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]acetic and 3‐[3‐Benzoyl‐2‐( tert ‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]propionic Acid, respectively The pure methyl esters 10 of the heterocyclic carboxylic acids specified in the title were prepared in several steps by known methods from aspartic and glutamic acid, with overall yields of ca. 20%. The corresponding heterocyclic acids 11 were doubly deprotonated by LiNEt 2 /BuLi or LiN(i‐Pr) 2 /BuLi to give enolatocarboxylates ( 3 ). The latter were reacted with electrophiles (MeOD, Mel, C 6 H 5 CH 2 Br) to give the crystalline products 14 – 21 diastereoselectively. Hydrolysis of the imidazolidinone ring of three such products gave the corresponding α‐branched aspartic and glutamic acids 22 – 24 of known absolute configuration, thus establishing the stereochemical course of the overall enantioselective alkylations.