Anthraquinone fused sulfolenoporphyrins: Regulation of reactivity and property through annulations

Abstract

The sulfolenoporphyrin-based Diels-Alder reaction is an efficient strategy in the construction of aromatic ring-fused porphyrins. However, the structure-reactivity relationship is still less explored. Here, we have synthesized the mono-, bis- and tri-anthraquinone fused sulfolenoporphyrins and explore the effect of anthraquinone fusion on their further Diels-Alder reactions. As a result, more anthraquinone fusions lead to higher reactivity but lower annulation yield. Theoretical calculation discloses that anthraquinone fusion has the HOMO of the dienes (i.e., the intermediates after extrusion of SO2 from sulfolenoporphyrins) raised owing to the [Formula: see text]-extension, affording high reactivity. However, as the number of ring fusions increases, the LUMO energy levels of dienes are reduced, which seems to benefit the side reaction (i.e., the dimer/oligomerization owing to the Diels-Alder reaction among porphyrin dienes), leading to the rapid consumption of dienes and low yields. Besides, the influence of the peripheral anthraquinone units on molecular stacking, absorption as well as aromaticity was investigated experimentally and computationally. In brief, this work has investigated the structure-reactivity relationship of sulfolenoporphyrins in the Dies-Alder reaction, which will help construct [Formula: see text]-extended porphyrin rationally.