For many years our research group’s interest lies in the study of nucleophilic/electrophilic aromatic substitution reactions. We found that when strongly activated substrates are used for mechanistic studies, the classical rules related to the steps involved in this kind of reactions are not always followed. The steps involved in both reactions are the formation of sigma-complexes which are usually not isolable because of their instability, bringing them to a rapid conversion into substitution products. However, when we used strongly activated species, namely superelectrophiles and supernucleophiles, we have been able to identify, and in some cases to isolate, the related Wheland, Meisenheimer or sigma-complexes that are contemporaneously Wheland and Meisenheimer intermediates. a,b These intermediates are moderately stable and have been identified at low temperature by NMR spectroscopy. On the basis of these findings, we recently developed another supernucleophilic compound (2,4-dipyrrolidinyl-1,3-thiazole (DPT)), which readily reacts with both superelectrophiles 4,6-dinitrotetrazolepyridine (DNTP) and 4,6-dinitrobenzofuroxan (DNBF) to form stable Wheland-Meisenheimer complexes (respectively WM1 and WM2) that we were able to isolate and crystallize, obtaining interesting information from their X-Ray diffraction analysis.2 A theoretical study of these reactions provided us important data about the reaction pathways and the great stability of these complexes. Nowadays we are studying the reactivity of DPT towards other superelectrophiles to give more informations on the WM complexes and to investigate the mechanisms of aromatic substitution reactions. . a) Boga, C.; Del Vecchio, E.; Forlani, L. Eur. J. Org. Chem. 2004, 1567–1671; b) Boga, C.; Del Vecchio, E.; Forlani, L.; Mazzanti, A.; Todesco, P. E. Angew. Chem. Int. Ed. 2005, 44, 3285–3289. 2. Forlani, L.; Boga, C.; Mazzanti, A.; Zanna, N. Eur. J. Org. Chem., in press.

Trapping and analyzing Wheland-Meisenheimer sigma-complexes, usually labile and escaping intermediates

ZANNA, NICOLA;BOGA, CARLA;FORLANI, LUCIANO
2011

Abstract

For many years our research group’s interest lies in the study of nucleophilic/electrophilic aromatic substitution reactions. We found that when strongly activated substrates are used for mechanistic studies, the classical rules related to the steps involved in this kind of reactions are not always followed. The steps involved in both reactions are the formation of sigma-complexes which are usually not isolable because of their instability, bringing them to a rapid conversion into substitution products. However, when we used strongly activated species, namely superelectrophiles and supernucleophiles, we have been able to identify, and in some cases to isolate, the related Wheland, Meisenheimer or sigma-complexes that are contemporaneously Wheland and Meisenheimer intermediates. a,b These intermediates are moderately stable and have been identified at low temperature by NMR spectroscopy. On the basis of these findings, we recently developed another supernucleophilic compound (2,4-dipyrrolidinyl-1,3-thiazole (DPT)), which readily reacts with both superelectrophiles 4,6-dinitrotetrazolepyridine (DNTP) and 4,6-dinitrobenzofuroxan (DNBF) to form stable Wheland-Meisenheimer complexes (respectively WM1 and WM2) that we were able to isolate and crystallize, obtaining interesting information from their X-Ray diffraction analysis.2 A theoretical study of these reactions provided us important data about the reaction pathways and the great stability of these complexes. Nowadays we are studying the reactivity of DPT towards other superelectrophiles to give more informations on the WM complexes and to investigate the mechanisms of aromatic substitution reactions. . a) Boga, C.; Del Vecchio, E.; Forlani, L. Eur. J. Org. Chem. 2004, 1567–1671; b) Boga, C.; Del Vecchio, E.; Forlani, L.; Mazzanti, A.; Todesco, P. E. Angew. Chem. Int. Ed. 2005, 44, 3285–3289. 2. Forlani, L.; Boga, C.; Mazzanti, A.; Zanna, N. Eur. J. Org. Chem., in press.
SIGMA-ALDRICH YOUNG CHEMISTS SYMPOSIUM 11° SAYCS (Atti)
O15
O15
N. Zanna; C. Boga; L. Forlani
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/108482
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