Catalyst-free Diels–Alder reactions of vinylphosphonates with cyclopentadienones

The unprecedented thermal Diels–Alder reaction of the diethyl vinylphosphonate and diethyl styrylphosphonate with various cyclopentadienones is described. In these Diels–Alder reactions, catalysis was not required and the corresponding cycloadducts derivatives were obtained. The tetraethyl vinylidene-1,1-bis-phosphonate was found to be less reactive than monophosphonates with the same cyclopentadienones.