Biomimetic synthesis, inspired by direct and fast biosynthetic processes, is an efficient way to produce complex natural products. This thesis doctoral work focused on the development of collective strategies, from biomimetic intermediates, to get a quick access to three families of diketopiperazines: gliocladrides (functionalized DKPs), quinazolino-DKPs and oxepino-DKPs. The late-stage chemical oxidation reactions and microbial transformations on the two first intermediates were envisaged to synthesize gliocladrid A and oxepino-DKPs. A regioselective late-stage oxidation operated by DDQ was discovered, bringing new synthetic possibilities to make aurantiomides in a collective manner. An alternative methodology to synthesize oxepino-DKPs was investigated in the meantime. A temperature-controlled tandem cyclopropanation/oxa-Cope rearrangement was developed successfully to prepare 2,5-dihydrooxepines. This method was afterwards elucidated by experimental and computational (DFT) studies and further applied as the key step to finish the intractable total synthesis of radulanins. This oxa-Cope rearrangement approach also led to achieve the installation of 2,5-dihydrooxepine DKP, getting close to the accomplishment of the total synthesis of cinereain.