Synthesis, properties and reactivity of an ortho-phenylene-cyclopentene-bridged tetrapyrrole

Abstract

Increasing the number of meso-methine carbons of porphyrin has led to a creation of a series of vinylogous expanded porphyrins, while the introduction of an ortho-phenylene-unit as a pyrrole-connecting two-carbon bridge usually leads to prevention of effective macrocyclic conjugation. Cyclopentene can serve as a conjugative bridge to increase the macrocyclic conjugation owing to its cis-geometry. In this work, ortho-phenylene-cyclopentene-bridged tetrapyrrole 5 was prepared on the basis of a coupling strategy. The tetrapyrrole 5 exhibited slightly more conjugative features as compared to ortho-phenylene-bridged tetrapyrrole 4. Oxidation of 5 with [bis(trifluoroacetoxy)iodo]benzene (PIFA) at low temperature afforded a partly fused tetrapyrrolic compound 9 having a spiro-connected pyrrolo[2, 1-a]isoindole moiety.