Synthesis of Dipeptides Containing Novel Cyclopropyl‐ and Cyclopropenyl‐Substituted β‐ and γ‐Amino Acids

The N ‐silylated methyl 2‐aminocyclopropanecarboxylate 1 can be incorporated into a dipeptide via a CsF‐mediated condensation reaction with N ‐tosylated phenylalanine chloride 5 . Due to its instability the corresponding free β‐amino acid 4 could not be isolated up to now, and peptides containing this structural element have previously not been accessible. After desilylation, the aminomethyl‐substituted cyclopropane or cyclopropene derivatives trans ‐ 10, 12 , and 13 also provided N ‐protected dipeptides in good yields.