1,3-Diphenylisoindole and 1,3-diphenyl-2-methylisoindole have been prepared by Leuckart reactions of o-di-benzoylbenzene and ammonia or methylamine. 1,3-Diphenylisoindole gives stable Diels-Alder addition products with acetylene dicarboxylic ester and benzyne, but the adduct with maleic anhydride readily reverts to the starting materials. 1,3-Diphenylisoindole can also be prepared by base treatment