Substituent effect on the selectivity of [3.3]Orthoanthracenophanes in the Diels-Alder reaction with N-(p-substituted phenyl)maleimides

Diels-Alder reactions of benzo- and naphtho-[3.3]orthoanthracenophanes 1a-b with N-(p-nitro, chloro or methoxy-substituted phenyl) maleimides 2a-c were investigated. In most cases, approximately equal amounts of inside-adduct 3 and outside-adducts (4 + 5) were obtained except for the outside-selective addition reaction of naphthophane 1b with p-nitro derivative 2a. Of the outside- the endo-adduct 4 was formed predominantly in all cases. Especially, the reaction of 1b afforded endo-adducts 4ba-bc almost exclusively. These facts suggest that the interaction between the phenyl group of 2 and the part of the anthraceno-unit closest to the underlying naphtho/benzo-moiety of 1 leads to a greater tendency toward endo-orientation.