Molecular diversity in cyclization of Ugi-products leading to the synthesis of 2,5-diketopiperazines: computational study

Ugi-adducts were obtained via a one-pot four-component reaction of divergent aldehydes, amines, aroylacrylic acids and isocyanide in methanol. These products were subjected to intramolecular Michael addition in the presence of K2CO3 in DMF at room temperature to afford a single product. Literally, the formation of two heterocyclic systems, 6-membered diones or 7-membered diones are possible, which could not be identified by conventional spectroscopic methods. The X-ray crystallographical data was obtained for one selected product, which indicated preferential formation of the corresponding 6-membered dione. In order to establish the generality of this mode of cyclization, the quantum chemistry calculations were performed. The obtained results confirmed the favorable formation of 6-membered diones in the gas and also several solution phases. All the products were screened for their antibacterial and antifungal activities.