Allyl ester as temporary protecting group for the β‐carboxy function of aspartic acid

The use of the allyl ester as a temporary protecting function in aspartyl peptides is described. The β‐allyl ester was introduced into Boc‐Asp‐Phe‐NH2 4a, Boc‐Asp‐Gly‐NH2 4b and Boc‐Asp‐Ser‐NH2 4c by means of the caesium salt method. It was removed from these molecules 5 using noble metal catalysts under weakly basic, acidic or even neutral conditions likewise in high yield. The formation of an aminosuccinyl derivative during the deblocking reactions was not observed. Treatment of the dipeptide Boc‐Asp(OAll)‐AS‐NH2 with an excess of triethylamine at room temperature induced the ring closure to the cyclic imide.