Propellanes. Part LXXI. Confirmation of predicted regiospecificity in Diels-Alder reactions of certain propellanes with 4-phenyl-1,2,4-triazoline-3,5-dione

Two isomeric propellane epoxides 1a and 1b containing a cyclohexadiene ring are attacked by the title dienophile as predicted, syn to the five-membered ether ring whose α-hydrogens exert less repulsion than the α-epoxy hydrogens or the epoxide oxygen, respectively, of the cyclobutane ring.