Synthesis of meso-substituted corroles and porphyrins using iodine as a catalyst
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J. Chem. Sci. (2020) 132:123 https://doi.org/10.1007/s12039-020-01823-z
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Synthesis of meso-substituted corroles and porphyrins using iodine as a catalyst ANSHU DANDIA and SHIVE M S CHAUHAN* Bio-Organic Research Laboratory, Department of Chemistry, University of Delhi, Delhi 110 007, India E-mail: [email protected] MS received 15 March 2020; revised 11 June 2020; accepted 12 June 2020
Abstract. Different types of corroles and porphyrins are synthesized from substituted aldehydes and pyrrole. The current synthetic method involves iodine as catalyst and proceeds at room temperature itself. By varying the amounts of reactants (i.e., pyrrole and aldehydes), the corrole and porphyrins were obtained in good to excellent yields. These products were characterized by 1H-NMR, UV-visible, and HRMS techniques. The reaction approach utilizes the readily available pyrrole and substituted aldehydes as starting materials and makes this reaction highly attractive in diversity-oriented synthesis. Keywords. Pyrrole; aldehydes; iodine; corrole; corrin; porphyrin.
1. Introduction Porphyrins are the class of tetrapyrrolic macrocycles comprising of four pyrrole rings that are linked through the meso-carbon atoms at meso-positions.1 These are comprised of 18p electronic conjugated system in which 18p electrons are delocalized over 20 atoms.2 It also contains 22p electrons, but their 18p electrons form a planar structure and are responsible for their aromaticity. Metalloporphyrin ring is common in a variety of important biological system where it is responsible for the activity of that system.3 Porphyrins are colored in nature and are characterized by their characteristic UV-visible absorption pattern. Recently, the porphyrins and metalloporphyrins were used in photodynamic therapy,4 solar cells,5 chemical sensors,6 catalysts,7 dyes and pigments,8 liquid crystals9, etc. Corroles are fully aromatic tetra-pyrrolic organic macrocyclic compounds that are analogues of porphyrins.10 It is a 19-carbon containing compound (one less than porphyrin), which possesses 18p conjugated electronic system.11 Similar to other porphyrins and their analogues, corroles are aromatic in nature.12 However, corrole’s skeleton possesses a direct pyrrole–pyrrole linkage13 at each meso-carbon
atom of porphyrin skeleton. Moreover, in solutions, corroles are present in acid–base equilibria and lead to the formation of cationic or anionic species by reacting with acid or base. The presence of one imine-like and three pyrrole-like nitrogen donor atoms make them more acidic (stronger acid) than their porphyrin and corrin analogues.14 Due to the alteration of ligands structure, the transition metal complexes of corroles show very different properties than the analogous metalloporphyrins. As compared to the diprotonic porphyrins, corroles behave as tetradentate trianionic ligands toward transition metal ions.15 Thus, it helps them to stabilize the unusually high oxidation states, such as cobalt
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