International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018

Recent Developments in Synthesis

Anil Kumar Department of Applied Chemistry, Delhi Technological University

ABSTRACT New synthetic methods for the synthesis of have been discussed in details. Corrole are very robust molecule and are extensively used in metallocatalyst. Keywords: Corrole, Synthesis, Recent

1. INTRODUCTION Corrole is considered as a member of corrinoid family. Corrinoids are a group of compounds containing four reduced pyrrole rings joined into a macrocyclic ring by links betweena position, three of these links are formed by a one carbon unit and the other by a direct Cα-Cα bond.They include various vitamins B12 factors and related derivatives bases upon the skeleton of C19H24N4. The atoms are numbered and the rings are lettered as shown in figure 1.4. The numbering is the same that of nucleus. Number 20 is omitted in corrole and corrin ring to retain comparability with the inner core nitrogen atoms numbered from 21 to 24. In the corrole structure, the imino nitrogen atom is located at position 24.The major structural differences of corrole to porphyrin are that the corrole have a somewhat more condensed N4 coordination core (i.e. inner cavity size smaller), act as trianionic rather than dianionic ligands, and are of lower symmetry (C2v). The synthesis of corrole is very tedious process and results in low yield. Since after the discovery of new methodologies developed by Gross et. al. in 1999, there is tremendous increase in the literature of corroles and their applications. Herein, we are giving brief outline of synthetic approaches adopted [1].

2. SYNTHETIC APPROACHES OF CORROLE The interesting structure of corrole remained as a synthetic challenge. The synthesis of β-substituted corroles dates back to the historic efforts to prepare . Such synthesis involved inconvenient stepwise procedures. Unlike the case with porphyrin, synthesis of meso-submitted corroles from readily available starting materials did not exist prior to the late 1990’s. Until 1999, corrole synthesis was quite difficult. [2-5]. The following methods were used prior to 1999. 2.1: SYNTHESIS FROM BIPYRROLIC UNITS. The condensation of dipyrromethene and a bipyrrole unit provides a route for the formation of corrole macrocycle through “2+2” approach. This method was reported by Johnson and coworkers. [6]. In this method, condensation occurs in presence of acid followed by reaction with cobalt(II) acetate and triphenylphosphine give rise to the corresponding corrole complex. It was found that cobalt is necessary for the tetramerization of ring as no corrole formation occur in the absence of cobalt ion which was studied by Vogel and coworkers. [7] 2.2 SYNTHESIS FROM A, C-BILADIENES The most general method to synthesize corroles was cyclization of a, c-biladienes. This tetrapyrrolic precursor is generally obtained as a crystalline dihydrobromide salt by condensation of a dipyrromethene dicarboxylic acid with two equivalents of 2-formylpyrrole in the presence of hydrogen bromide. [8]. During the first synthesis of corrole, cyclization of a, c-biladienes occur photochemically in basic medium. Later, it was 1593 Anil Kumar International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 5, Issue 3 March 2018 investigated that basic conditions were always necessary to allow the cyclization of a, c-biladienes even in the absence of irradiation. [9] 2.3 SYNTHESIS FROM 2-SUBSTITUTED PYRROLE In this method, substituted pyrrole i.e. 2-(a-hydroxy-benzyl)pyrrole was first reacted in acidic ethanol which was followed by the reaction with cobalt(II) acetate in the presence of triphenylphosphine to produce penta- coordinated cobalt complex. Only Cobalt ion has shown such template effect. Such hypothesis was given that the formation of corrole occurred by the ring contraction of porphyrinogen(intermediate) that was catalyzed by the cobalt ion. This reaction is analogous with the biochemical synthesis of the corrin of Vitamin B12from uroporphyrinogen III. [10] 2.4 SYNTHESIS BY MACROCYCLIC RING CONTRACTION This method involved the formation of corrole by an electrocyclic reaction involving loss of sulfur from a nonaromatic intermediate, the meso-thiaphlorin. This meso-thiaphlorin macrocycle was synthesized from “2+2” acidic condensation of a dipyrrylsulfide dialdehyde with dipyrromethene [11]. This ring contraction method has not been further developed because of the difficulty in the synthesis of sulfur containing starting materials. Before 1999, the synthesis of corrole remained quite a difficult task. But, in year 1999, paolesse [4- 5] and Gross [1] who each reported one-pot, facile synthetic methodologies for the synthesis of corroles bearing three identical substituents at meso position from the reaction pyrrole with an aldehyde. These facile methods are: 2.5 SOLVENT FREE CONDENSATION Gross [1] reported a new approach in which solvent free condensation occurs between pyrrole and aldehydes. The reaction condition consists of heating of mixer of pyrrole and aldehyde in equimolar ratio on a solid support like silica or alumina for few hours, followed by its oxidation by DDQ.

REFERENCES: 1. Gross, Z.; Galili, N.; Saltsman, I. Angew. Chem. Intl. Ed. 1999, 38, 1427. 2. Woodward, R.; Hoffman, R. Angew. Chem. Intl. Ed. 1969, 8, 71. 3. Rose, E.; Kossyani, A. J. Am. Chem. Soc. 1996, 118, 1567. 4. Paolesse, R.; Boschi, T.; Inog. Chim. Acta1993, 203, 107. 5. Licoccia, S.; Paolesse, R. J. Org. Chem. 1998, 63, 3190. 6. Conlon, M.; Johnson, A. W. J. Chem. Soc. Perkin Trans. 1973, 2281. 7. Vogel, E.; Broring, M.; Angew. Chem. Intl. Ed. 1995, 34, 2511. 8. Johnson,A. W.; Kay, I. T. J. Chem. Soc, 1965, 1620. 9. Dolphin, D. J. Chem. Soc. B, 1966, 880-885. 10. Rasetti, V.; Pfaltz, A.; PNAS, USA, 1981, 78, 16. 11. Johnson, A. W.; Kay, I. T. Chem. Comm., 1970, 807. 12. Narayana, S. J.; Chandrashekhar, T. K.; Org. Lett. 1999, 1, 587. 13. Cho, W. S.; Lee, C. H. Tett. Lett. 2000, 41, 497. 14. Simkhovich, L.; Gross, Z. Inorg. Chem. 2002, 41, 5433.

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