UNEXPECTED FORMATION OF DIENES IN THE DIELS-ALDER REACTION OF EXOCYCLIC 1-BROMOBUTADIENES OF POLYCYCLIC-HYDROCARBONS

Polycyclic dienes having an exocyclic 1-bromobutadiene moiety react wi th dienophiles and fullerene-C-60 to afford exclusively dienes via a c ycloaddition-elimination mechanism. Neither the primary adducts nor th e double addition products derived from a second cycloaddition of the dienophile to the diene could be detected. In one case only, i.e. with 4-phenyl-1,2,4-triazoline-3,5-dione, was the double addition product formed. Contrary to expectations, X-ray diffractometric analysis shows that this adduct is formed following a contrasteric approach.