Facile Peripheral Functionalization of Porphyrins by Pd-Catalyzed [3+2] Annulation with Alkynes

Abstract

Going round the outside: The palladium-catalyzed coupling of meso-bromoporphyrins with a variety of internal alkynes efficiently provides peripherally cyclopentadiene-fused porphyrins. This modification has a significant impact on the electronic system of the porphyrin rings (see scheme), which results in non-porphyrin-like absorption spectra and narrower HOMO–LUMO gaps. Oxidation of the outer CC bond is facilitated by the induced strain.