Facile peripheral functionalization of porphyrins by Pd-catalyzed [3+2] annulation with alkynes

Abstract

(Chemical Equation Presented) 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. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.