REGIOSELECTIVE AND FACIAL-SELECTIVE EFFECTS OF ALLYLIC HETEROATOMS IN 1,3-DIPOLAR CYCLOADDITION OF A NITRILE OXIDE

The 1,3-dipolar cycloaddition of nitrile oxides to 2-X-bicyclo[2.2.2]oct-5-enes (X=0, NMe, S, SO2) were investigated together with acyclic and alicyclic analogues. The regioselectivity in an exo-attack was controlled by the heteroatom present at an allylic position - a remote attack was predominant in the cases of O and SO2 but a vicinal attack in those of NMe and S- and the results were rationalized from the electronic nature of the heteroatom, X. In an endo-attack, a remote attack was observed in every case and the dipole-dipole repulsion between X and the oxygen of the nitrile oxide was considered to be a predominant factor. The steric environment around the heteroatom controled the facial-selectivity. © 1990 The Chemical Socity of Japan.