Abstract
Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true “in water” organocatalytic conditions. The highly insoluble catalyst aggregates can easily be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield.
Highlights
The highly insoluble catalyst aggregates can be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield
Catalysis is a key concept in contemporary chemistry, with far-reaching implications in several fields ranging from molecular biology to the sustainable large-scale synthesis of drugs, agrochemicals, or functional materials
N-Boc-(S)-prolinal 44 with with benzaldehyde benzaldehyde and and pyrrole, pyrrole, mixed we found after careful chromatographic purification of theofcrude reaction mixture, the desired we foundthat thateven even after careful chromatographic purification the crude reaction mixture, the compound was always obtained together with the corresponding
Summary
Catalysis is a key concept in contemporary chemistry, with far-reaching implications in several fields ranging from molecular biology to the sustainable large-scale synthesis of drugs, agrochemicals, or functional materials. Scheme 1.1.pH-switchable aminocatalysts based on in situ of amphiphilic pH-switchable aminocatalysts based onaggregation/dissociation in situ aggregation/dissociation of porphyrins These amine-porphyrin amine-porphyrin hybrids hybrids can can readily readily be be prepared, prepared, albeit albeit in relatively relatively low overall overall yields, yields, by a mixed-porphyrin synthesis [15] from pyrrole, benzaldehyde, and a suitable suitable N-Boc-protected. Weprocesses) thought that it would be interesting weight orthrough by micellar through “on water” We thought that it to introduce chiralityto inintroduce our amphiphilic amine-porphyrin hybrids, in order to evaluate would be interesting chiralitysecondary in our amphiphilic secondary amine-porphyrin hybrids, in the induction degree of that asymmetric that could organocatalytic be achieved inaldol aqueous theorder degreetoofevaluate asymmetric could be induction achieved in aqueous and organocatalytic aldol and Michael reactions
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