N. Defacqz et al., DIELS-ALDER REACTIVITY OF TRIALKYL 2-PHOSPHONOACRYLATES WITH N-BUTA-1,3-DIENYLSUCCINIMIDE, Perkin transactions. 2, (10), 1997, pp. 1965-1968
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 th
e succinimido and phosphonate groups respectively has been established
by NMR and X-ray diffraction analyses. Triethyl 2-phosphonoacrylate 2
b similarly undergoes cycloaddition with the diene 1 to give a 55:45 m
ixture of ortho stereoisomers 3b (cia axial/equatorial) and 4b (trans
axial/axial). The activating and directing effect of the phosphonate g
roup is discussed on the basis of a theoretical approach considering t
he van der Waals complexes.