Improved Synthesis of <i>ortho</i>‐Phenylene‐bridged Cyclic Tetrapyrroles and Oxidative Fusion Reactions Toward Substituted Tetraaza[8]circulenes
Yuki Morimoto, Fengkun Chen, Yusuke Matsuo, Koki Kise, Takayuki Tanaka, Atsuhiro Osuka
Abstract
Hetero[8]circulenes have emerged as novel functionalized heteronanographenes that show various promising functions such as bright fluorescence, charge transporting, and redox reactivities. One of the effective synthetic strategy is the fold-in type oxidative fusion reaction of ortho-phenylene-bridged cyclic tetrapyrroles, whose construction, however, is not well-sophisticated in terms of reproducibility and possibility for versatile derivatization. In this paper, a "reverse" coupling strategy has been developed, which enabled synthesis of opp-type low symmetric analogues of cyclic tetrapyrroles. Oxidative fusion reaction conditions to afford tetraaza[8]circulenes have also been reinvestigated and improved. Substituent effects of cyclic tetrapyrroles and tetrabenzotetraaza[8]circulenes are studied for solid-state structures and packing structures, redox potentials, and optical properties.