Two tandem processes involving the cycloaddition of benzynes have been developed for the synthesis of polyaromatic hydrocarbons. Benzynes react with fluorene-derived alkenes through a tandem Diels-Alder reaction/dehydrogenation process to afford benzo[ b]fluoranthenes in 35-87% yields. In addition, an unprecedented [2 + 2] cycloaddition/ring-opening sequence of benzynes and fluorene-derived N-arylimines provides facile access to spiroacridines in 38-79% yields.