H-1 and C-13 NMR spectroscopy has been used to detect and to characterize the adducts formed, in alkaline solutions, by the attack of dithionite anion on 3-carbamoyl or 3-cyano substituted pyridinium salts. In all studied cases, only 1,4-dihydropyridine-4-sulfinates, formed by attack of dithionite oxyanion on the carbon 4 of pyridinium ring, were found. This absolute regioselectivity seems to suggest a very specific interaction between the pyridinium cation and the dithionite through the formation of a rigidly oriented ion pair, determining the position of attack. In weak alkaline solution, the adducts decompose according to two mechanisms S(N)i and S(N)i ': the SNi path is operative in all studied cases and preserves the 1,4-dihydro structure yielding the corresponding 1,4-dihydropyridines, whereas the S(N)i ' path involves the shift of 2,3 or 5,6 double bonds yielding 1,2- or 1,6-dihydropyridines, respectively. The formation of 1,2- or 1,6-dihydropyridines, in addition to 1,4-dihydro isomers, depends on their respective thermodynamic stabilities. (c) 2005 Elsevier Ltd. All rights reserved.

Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition / Vincenzo, Carelli; Felice, Liberatore; Scipione, Luigi; Barbara Di, Rienzo; Tortorella, Silvano. - In: TETRAHEDRON. - ISSN 0040-4020. - STAMPA. - 61:43(2005), pp. 10331-10337. [10.1016/j.tet.2005.07.096]

Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition

SCIPIONE, Luigi;TORTORELLA, Silvano
2005

Abstract

H-1 and C-13 NMR spectroscopy has been used to detect and to characterize the adducts formed, in alkaline solutions, by the attack of dithionite anion on 3-carbamoyl or 3-cyano substituted pyridinium salts. In all studied cases, only 1,4-dihydropyridine-4-sulfinates, formed by attack of dithionite oxyanion on the carbon 4 of pyridinium ring, were found. This absolute regioselectivity seems to suggest a very specific interaction between the pyridinium cation and the dithionite through the formation of a rigidly oriented ion pair, determining the position of attack. In weak alkaline solution, the adducts decompose according to two mechanisms S(N)i and S(N)i ': the SNi path is operative in all studied cases and preserves the 1,4-dihydro structure yielding the corresponding 1,4-dihydropyridines, whereas the S(N)i ' path involves the shift of 2,3 or 5,6 double bonds yielding 1,2- or 1,6-dihydropyridines, respectively. The formation of 1,2- or 1,6-dihydropyridines, in addition to 1,4-dihydro isomers, depends on their respective thermodynamic stabilities. (c) 2005 Elsevier Ltd. All rights reserved.
2005
adduct decomposition; dihydropyridines; dithionite adducts; pyridinium salts; s(n)i ' and s(n)i ' mechanisms; sni and sni′ mechanisms
01 Pubblicazione su rivista::01a Articolo in rivista
Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition / Vincenzo, Carelli; Felice, Liberatore; Scipione, Luigi; Barbara Di, Rienzo; Tortorella, Silvano. - In: TETRAHEDRON. - ISSN 0040-4020. - STAMPA. - 61:43(2005), pp. 10331-10337. [10.1016/j.tet.2005.07.096]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/235032
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