A Facile Palladium‐Mediated Contraction of Benzene to Cyclopentadiene: Transformations of Palladium(II) <i>p</i>‐Benziporphyrin

Abstract

Feeling the contractions: Addition of palladium(II) and a hydroxide ion to a C–C double bond, β elimination, and competing cheletropic extrusion of carbon oxide and 1,2-hydride shift reactions lead to the contraction of p-phenylene to form a cyclopentadiene unit. This reaction results in the formation of a 21-carbaporphyrin from a palladium(II) p-benziporphyrin (see picture; C red/gray, N blue, Pd orange).