Expanded Porphyrin Contraction: From [22]Triphyrin(6.6.0) to [22]Triphyrin(6.5.0)

An expanded triphyrin containing a bipyrrole moiety and annulene links, namely tetraphenyl-22]triphyrin(6.5.0), 2 , has been synthesized. The synthesis proceeded by a postsynthetic transformation of tetraphenyl-22]triphyrin(6.6.0), 1 , in a metal-free unexpected and unprecedented ring contraction during column chromatography on alumina. The observed transformation, located at the hydrocarbon chain linking the pyrrole units, formally corresponds to a subtraction of one carbon atom from an annulene circuit. In contrast to the flexible substrate 1 , the product 2 is conformationally rigid, and capable of chloride anion binding in its protonated form.