STEREOCHEMICAL PI-FACIAL SELECTIVITY OF THE DIELS-ALDER REACTION OF BENZ[A]ACEANTHRYLENE AND 1,4-DIPHENYLBENZ[A]ACEANTHRYLENE

The Diels-Alder (D-A) reaction of the twisted hydrocarbon 1,4-diphenyl benz[a]aceanthrylene (4) with dienophiles maleic anhydride, bromomalei c anhydride, and N-phenylmaleimide and with benzyne is reported. The s tereochemistry of the products derived from the D-A reaction of 4 is c ompared with the products derived from reaction of planar benz[a]acean thrylene (5) with maleic anhydride as a model. The endo regiochemical pi-facial selectivity of 4 appears to be the result of the steric effe ct of a phenyl substituent as the transition state is reached. Compoun d 5 produces both endo and exo D-A adducts when treated with maleic an hydride, X-ray crystallographic analysis verifies the topology of the bromomaleic anhydride adduct of 4 and the maleic anhydride adduct of 5 .