Diels-Alder reactivity of trialkyl 2-phosphonoacrylates with N-buta-1,3-dienylsuccinimide

N-Buta-1,3-dienylsuccinimide 1 reacts quantitatively with trimethyl 2-phosphonoacrylate 2a to furnish the ortho-[4 + 2]-cycloadduct 3a as a single stereoisomer. The cis axial/equatorial. relationship between the succinimido and phosphonate groups respectively has been established by NMR and X-ray diffraction analyses. Triethyl 2-phosphonoacrylate 2b similarly undergoes cycloaddition with the diene 1 to give a 55:45 mixture of ortho stereoisomers 3b (cia axial/equatorial) and 4b (trans axial/axial). The activating and directing effect of the phosphonate group is discussed on the basis of a theoretical approach considering the van der Waals complexes.