Centrohexacyclic or “K5” Molecules: Development of a Growing Family of Topologically Nonplanar Organic Compounds

This article gives a comprehensive review of the synthetic development of centrohexacyclic organic compounds (“centrohexacyclanes”) during the past decade. With their unique feature of having a molecular constitution that corresponds to the complete graph K5, centrohexacyclanes represent the majority of the rare class of topologically nonplanar compounds. Starting from the few previously known organic, element–organic and inorganic K5 compounds, the syntheses of various organic centrohexacyclanes are discussed, based mainly on three different strategies that have emanated from the chemistry of centropolyindanes: the propellane, fenestrane, and “broken fenestrane” routes. In addition, the first results of some targeted transformations of centrohexaindane, the Td‐symmetrical hexabenzoannelated centrohexaquinane, are presented.