Diindenopyrenes: Extended 1,6- and 1,8-Pyrenoquinodimethanes with Singlet Diradical Characters.

Diindenopyrene 4b and its diastereomer, which are extended homologues of 1,6- and 1,8-pyrenoquinodimethanes fused by indene units, respectively, were synthesized by reaction of 1,4,5,8-tetrakis(mesitylethynyl)naphthalene (7) with bis(2,4,6-trimethylpyridine)iodine(I) hexafluorophosphate via cationic cyclization mechanisms at both centers of reaction. Unexpectedly, reaction of 7 with iodine, a reagent that typically gives products of cationic cyclization, gave cycloheptapentalenoindenophenalene derivative 9b and its diastereomer incorporating an azulene unit at one end of the π framework, via two different modes (radical and cationic) of cyclization at each reaction site. The physical properties of the products are presented, and the dual modes of cyclization of 7 and its model compound with only one reaction center are discussed.