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Corroles programmed for regioselective cycloaddition chemistry — synthesis of a bisadduct with C60-fullerene

“…When compared to the four methylene singlets of 4, two of the signals (at 4.27 and 4.29 ppm) did not move significantly in the spectrum of 7, while two broad singlets at 4.92 and 5.99 ppm occurred at a significantly lower field (see Figs 3 and 4). As expected[4,5], the methylene protons next to the fullerene units were de-shielded and gave rise to the (broad) singlets at 4.92 and 5.99 ppm. Each one of these methylene signals correlated to a different carbon with resonances at 41.2 or at 42.4 ppm, i.e.…”

“…The corroles 4-6 thus represent heteroaromatic systems "programmed" for regioselective cycloaddition chemistry at the periphery (see Scheme 4). The structure of the main product, the diadduct 7, indicated the "western" and directly linked pyrroles (rings A and D) to undergo SO 2 -extrusion with a decisively higher relative rate than their "eastern" counterparts in 4 (and than was observed for the corresponding tetra-b,b′-sulfoleno-porphyrin 1) [4,5]. From the observed regioselectivity of electrophilic substitution reactions [16,17] deconjugation of the p-systems of the pyrrole rings A and D can be deduced to be less un-favorable than at rings B and C. A similar reactivity pattern also applies to the here studied pericyclic reactions.…”

“…The porphyrinoids are also useful as catalysts [2], as photo sensitizers in dye-sensitized solar cells [3] and as versatile molecular "tectons" for the build-up of larger (supramolecular) assemblies [4]. To provide a general basis for the synthesis of more complex porphyrin assemblies by cycloaddition reactions, the tetrab,b′-sulfolenoporphyrin 1 was introduced as a symmetrical percursor to reactive "porphyrin-dienes" [5]. Upon heating 1 lost sulphur dioxide and underwent [4+2] cycloaddition reactions readily, up to four consecutive times, to result in novel (symmetric) porphyrinoid conjugates [6,7].…”

Cycloadditions

“…Addition products of the paradihydroxy derivative 65 can be easily oxidized to the corresponding benzoquinonelinked fullerene with DDQ [48]. In the latter case, a chromophore is covalently attached to C 60 (74,Scheme 4.8). The strong activation of the fluoro-substituted phenyl ring by the nitro-and keto-group enables nucleophilic additions to this adduct in very good to quantitative yields.…”

Panchromatic π‐Extended Porphyrins from Conjugation with Quinones

“…Symmetrical β,β′‐tetrasulfolenoporphyrins have been prepared in a metal‐free form ( 1 ‐ 2H ) and as the Zn II , Ni II and Cu II complexes 1–Zn , 1–Ni and 1–Cu (Scheme ) . They were proposed to be versatile, reactive building blocks, “programmed” for further covalent attachment of functional units .…”