Perfluoroacetylenephosphonates in Diels–Alder reactions: Synthesis of perfluoroalkylated heterocyclic and carbocyclic phosphonates

Diethyl 3,3,3-trifluoroprop-1-ynylphosphonate and diethyl 3,3,4,4,4-pentafluorobut-1-ynylphosphonate are obtained by the dehydration of the corresponding enols using P2O5–Et3N system as a dehydrating agent, affording acetylenes in 50–60% yield. By the reaction of these perfluoroacetylenephosphonates with acyclic and cyclic 1,3-dienes or diene-like heteroaromatic and aromatic compounds corresponding Diels–Alder cyclo- and bicycloadducts were prepared in good yields (65–90%). The reactivity of the dienes and acetylenes which depends on their structure, as well as the regioselectivity of the reaction are established.