Synthesis of Expanded Porphyrinoids with Azulene and Indene Subunits and an opp-Dioxadicarbaporphyrin from Fulvene Carbinols and a Dioxacarbatripyrrin.

Abstract

In an attempt to prepare quatyrin derivatives, which are hydrocarbon analogues of the porphyrins, azulene-appended fulvene carbinols were self-condensed in the presence of BF3·Et2O. Although these investigations failed to give structures related to quatyrin, expanded porphyrin analogues were obtained instead. In dichloromethane, the major macrocyclic product consisted of three fulvene units, but when chloroform was used as the reaction solvent, a tetrafulvene macrocycle was isolated. Self-condensation of a furan-appended fulvene alcohol gave trace amounts of an opp-dioxadicarbaporphyrin. An alternative route to this novel system was developed where a dioxacarbatripyrrin was condensed with an indene dialdehyde in the presence of HBr. The heterodicarbaporphyrinoid proved to have strong globally aromatic properties as assessed by 1H NMR spectroscopy, anisotropy of induced current density, and NICS calculations. In the presence of excess trifluoroacetic acid, an unstable aromatic cation was formed by C-protonation of an indene subunit. This species was also highly diatropic, and the 1H NMR spectrum gave an unusually high Δδ value of 17.46 ppm.