Conformation Governed Reactivity of Fused Thia-Sapphyrin Dimers Bearing Multiply Fused Heteroaromatic Rings

Suitable conformations and proper alignment of complex natural macrocycles are essential for achieving their unique properties. However, such artificial macrocycle prototypes are still limited due to synthetic difficulties. In this respect, directly linked porphyrin analog dimers display tunable conformations and intriguing properties, and thus, they may be employed as a class of promising platforms. Herein, we report that one-pot oxidative dimerization of thia-hydrosapphyrin 1 yields dimers, 2_anti and 2_syn, comprising a transoid-oriented plate-like bipyrrolo[1,2-a] indolylidene. The thiophene-containing tetrapyrrole arching subunits in 2 lie at the opposite (anti) and same (syn) sides of the plate, respectively. Meanwhile, multiply fused cisoid-orientated dimer 3 was also obtained; a polycyclic pyrrolo-bridged bipyrroloindole derivative tethered with fully π-conjugated bridges was formed. Notably, the anti-dimer 2_anti underwent subsequent oxidative fusion to furnish a further-fused [6.5.5.7.5.5.5.6]-octacyclic compound 4_anti. In contrast, the syn-orientated 2_syn could not be further fused due to the long distance between the potential reaction sites. This study provides a unique approach to the fused dimeric porphyrin analogs for potential near-infrared optical materials by a simple oxidation reaction. It also reveals the importance of conformation-modulated reactivity for constructing complex porphyrin arrays.