Atropisomers of meso Tetra(N‐Mesyl Pyrrol‐2‐yl) Porphyrins: Synthesis, Isolation and Characterization of All‐Pyrrolic Porphyrins

Atropisomerism has been observed in a variety of biaryl compounds and meso‐aryl substituted porphyrins. However, in porphyrins, this phenomenon had been shown only with o‐substituted 6‐membered aromatic groups at the meso‐position. We show herein that a 5‐membered heteroaromatic (N‐mesyl‐pyrrol‐2‐yl) group at the meso‐position leads to atropisomerism. In addition, we report a ‘one‐pot’ synthetic route for the synthesis of ‘all‐pyrrolic’ porphyrin (APP) with several N‐protection groups (Boc, Cbz, Ms and Ts). Among these groups, we found that only the Ms group gave four individually separable atropisomers of meso‐tetra(N‐Ms‐pyrrol‐2‐yl) porphyrin. Furthermore, the reductive removal of Cbz‐ was achieved to obtain meso‐tetra(pyrrol‐2‐yl) porphyrin. Thus, our synthetic procedure provides an easy access to a group of APPs and stable atropisomers, which is expected to expand the application of novel APP‐based materials.