Alkylations of Chiral Imidazolidinones Derived from Di‐ and Triglycine and Attempts at Cyclisations to Give Cycloisodityrosines

Abstract

AbstractDi‐ and triglycine derivatives (1–5) containing a 2‐tert‐butyl‐1,3‐imidazolidin‐4‐one moiety were prepared in rac. and enantiopure forms. By deprotonations with LiNR2 these imidazolidinones were converted to Li, Li2, and Li3 derivatives (H‐N) and the latter alkylated, preferably with the more reactive electrophiles (MeI, benzylic and allylic bromides). The diastereoselectivity at the endocyclic (imidazolidinone) position is always very high (>95:5), while it varies with respect to the newly formed stereocentres at the exocyclic positions (2:1 to >95:5). Three dozens of new di‐ and triglycine derivatives were thus prepared and fully characterised. Cyclisation attempts with seven different diaryl ethers (23, 29, 32, 35, 39, 44, 45), which are potential precursors of cycloisodityrosines, failed. The configurations of the products were assigned by X‐ray structure analysis (29, 40, 53), NMR analysis, and hydrolysis to the amino acid components, followed by GC analysis.