Synthesis of meso‐Free Decaphyrin(1.1.1.1.1.1.1.1.1.1) by a Hydrodebromination Protocol; Aromaticity and Solvent‐Polarity Dependent Conformational Change

A meso-free beta-bromodecaphyrin has been constructed by [2+3+2+3] type acid-catalyzed cross-condensation and subsequent oxidation. Hydrodebromination of this tetrabromodecaphyrin with NaBH4 in the presence of TMEDA and palladium catalyst afforded beta-unsubstituted doubly meso-free [46]decaphyrin(1.1.1.1.1.1.1.1.1.1) as the first example of beta-unsubstituted meso-free regular expanded porphyrins with the number of pyrrole units larger than eight. It exhibits distinct aromaticity originating from its 46 pi-conjugated electronic circuit and flexible conformational change between non-twisted and doubly twisted forms depending on the solvent-polarity. Their distinct conformations have been analyzed by combined experimental and theoretical investigations.