Starting from Boc-activated diketopiperazines, original bicyclic derivatives of trans- and cis-2-aminocyclopentanecarboxylic acid were prepared by using two stereospecific tandem reactions. One of them is a tandem transannular rearrangement of activated lactams/alkylation process leading to the stereoselective synthesis of suitably chiral pyrrolidine2,4-diones, allowing subsequent Michael-initiated ring closure, a simple and concise route to original multifunctionalized alicyclic β-amino esters.