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.