ALKYLATIONS OF CHIRAL IMIDAZOLIDINONES DERIVED FROM DIGLYCINE AND TRIGLYCINE AND ATTEMPTS AT CYCLIZATIONS TO GIVE CYCLOISODITYROSINES

Di- and triglycine derivatives (1-5) containing a 2-tert-butyl-1,3-imi dazolidin-4-one moiety were prepared in rac. and enantiopure forms. By deprotonations with LiNR(2) these imidazolidinones were converted to Li, Li-2, and Li-3 derivatives (H-N) and the latter alkylated, prefera bly with the more reactive electrophiles (Mel, benzylic and allylic br omides). 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 prep ared and fully characterised. Cyclisation attempts with seven differen t diaryl ethers (23, 29, 32, 35, 39, 44, 45), which are potential prec ursors of cycloisodityrosines, failed. The configurations of the produ cts were assigned by X-ray structure analysis (29, 40, 53), NMR analys is, and hydrolysis to the amino acid components, followed by GC analys is.