The dihydroisoindole approach to linearly annelated π-extended porphyrins

The dihydroisoindole strategy for the synthesis of linearly annelated π-extended porphyrins is a common approach to tetrabenzo-, tetranaphtho-, and tetraanthraporphyrins with variable functionality and substitution patterns. This method implies the use of a common type of precursors involving the 4,7-dihydroisoindole moiety, which are the closest possible stable relatives of the unstable isoindole, benzoisoindole and naphthoisoindole. A key feature of this strategy is the unprecedented mildness of the final oxidative aromatization step, which accounts for synthetic versatility, better functional group tolerance and high purity of the products. Many new linearly annelated π-extended porphyrins of the tetrabenzo-, tetranaphtho-, and tetraanthraporphyrin families were produced and characterized for the first time, including soluble planar and highly emissive 5,15-diaryl derivatives. The double bond of the dihydroisoindole fragment can also be useful for further modification of the porphyrin by means of addition of cycloaddition reactions, leading to new, previously inaccessible porphyins bearing multiple halide, hydroxy, or acetoxy groups at the periphery.