Multicomponent and Metal-Free Diels–Alder/Aromatization Approach to the Stereospecific Synthesis of E-(Hetero)Stilbenes and Diarylacetylenes

Herein, we present a novel and metal-free approach to the stereospecific synthesis of E-stilbenes. Starting from substituted 6-arylhexa-3,5-dien-2-ones, a multicomponent enolacetylation/intermolecular Diels-Alder reaction was performed using ethyl acetate as a green solvent. The obtained cycloadducts were then oxidized without purification to produce the stilbenic products in good yields (up to 67%) and with complete (E)-stereospecificity and regioselectivity. Moreover, heterostilbenes were synthetized using this approach, displaying the potential applications of this protocol in pharmaceutical and material sciences. The proposed methodology was further extended to the synthesis of diarylacetylenes, furnishing a new metal-free synthetic access to this important class of compounds. Furthermore, DFT calculations were performed confirming a concerted [4+2] reaction mechanism of the key ring-forming step. At last, the energetic analysis of the possible Transition States helps to shed some light on the experimentally observed total regio- and chemoselectivity