Unexpected Formation of Dienes in the Diels−Alder Reaction of Exocyclic 1-Bromobutadienes of Polycyclic Hydrocarbons
journal contributionposted on 12.01.1996, 00:00 by Sergio Cossu, Giancarlo Cuomo, Ottorino De Lucchi, Michele Maggini, Giovanni Valle
Polycyclic dienes having an exocyclic 1-bromobutadiene moiety react with dienophiles and fullerene-C60 to afford exclusively dienes via a cycloaddition−elimination mechanism. Neither the primary adducts nor the 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.