Stereoselective synthesis, NMR conformational study and Diels-Alder reaction of β-functionalized 1-acetylvinyl arenecarboxylates

Article abstract of DOI:10.1016/0040-4020(95)00140-4

A stereoselective synthesis of novel β-substituted 1-acetylvinyl arenecarboxylates 2a-2h, via the bromo derivative 4a, is described. Isomer Z was the only product formed. Low temperature NMR experiments showed an s-cis/s-trans (20:80) conformeric equilibrium, and also a restricted rotational C-N barrier in 2a. X-ray diffraction of the latter revealed a planar s-trans conformation. Alkene 4a proved to be more reactive than 2a-2h towards cyclopentadiene (6) and isoprene (11) in Diels-Alder additions, giving the corresponding adducts 10 and 14 in high stereo- and regioselectivity.