A Leopard Cannot Change Its Spots: Unexpected Products from the Vilsmeier Reaction on 5,10,15-Tritolylcorrole.

Fabrizio Caroleo,Daniel O Cicero,Beatrice Berionni Berna,Greta Petrella,Lorena Di Zazzo,Roberto Paolesse,Sara Nardis

doi:10.3390/molecules25163583

Fabrizio Caroleo, Daniel O Cicero + Show 5 more

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https://doi.org/10.3390/molecules25163583

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Abstract

The reaction of 5,10,15-tritolylcorrole with 3-dimethylaminoacrolein (3-DMA) and POCl3 gives a further example of the rebel reactivity of this contracted macrocycle. While no evidence was obtained for the formation of the expected β-acrolein corrole, the inner core substituted N21,N22-3-formylpropylcorrole and the 10-acrolein isocorrole were the reaction products. By increasing the temperature or the amount of the Vilsmeier reagent, the 10-isocorrole became the unique reaction product. The formation of the isocorrole by electrophilic attack of the Vilsmeier reagent to the 10-position of the corrole is unprecedented in the porphyrinoids field and it could pave the way for a novel route to the preparation of stable isocorroles.

Highlights

Corrole is one of the first synthetic porphyrin analogues reported in the literature, being one of the results of the Johnson’s group approach to Vitamin B12 synthesis [1]
In our previous studies on the Vilsmeier reaction on free base corroles, we observed a significant decomposition of the starting material [15]; it has been envisaged to first tackle the decomposition challenge by a modified synthetic protocol, forming the Vilsmeier reagent in
We have previously reported the preparation of meso-alkyl isocorroles by reaction of Grignard reagent with oxidized corroles [20]

Summary

Introduction

Corrole is one of the first synthetic porphyrin analogues reported in the literature, being one of the results of the Johnson’s group approach to Vitamin B12 synthesis [1]. The contracted molecular skeleton and the trianionic nature as ligand are two important characteristics that make corrole different with respect to the porphyrin counterparts, as well as its non-innocent character as ligand [9] or its facile oxidation [10]. These differences influence the corrole reactivity and its functionalization pathways: corroles for example are more reactive towards electrophilic reagents than porphyrins, allowing both the reaction on the corrole free base and a different regioselectivity. This feature can be an advantage because the macrocycle is not inactivated by core protonation [11], avoiding the need of metal complex intermediate, the reaction is always oriented on the macrocycle β-positions [12]

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