STEREOSELECTIVE SYNTHESIS, NMR CONFORMATIONAL STUDY AND DIELS-ALDER REACTION OF S-FUNCTIONALIZED 1-ACETYLVINYL ARENECARBOXYLATES

A stereoselective synthesis of novel beta-substituted 1-acetylvinyl ar enecarboxylates 2a-2h, via the bromo derivative 4a is described. Isome r Z was the only product formed. Low temperature NMR experiments showe d an s-cis/s-trans (20:80) conformeric equilibrium, and also a restric ted rotational C-N barrier in 2a. X-ray diffraction of the latter reve aled a planar s-trans conformation. Alkene 4a proved to be more reacti ve than 2a-2h towards cyclopentadiene (6) and isoprene (11) in Diels-A lder additions, giving the corresponding adducts 10 and 14 in high ste reo- and regioselectivity.