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Cyclisation of 2-chloro-N-(2-pyridinyl)nicotinamides to 5-oxo-5,6-dihydrodipyrido[1,2-a:3â ,2â -e]pyrimidin-11-ium chlorides

Authors:  De Souza, M.V.N.;  Fernandes, E.L.; Pais, K.C.; Vasconcelos, T.A.; Wardell, S.M.S.V.; Wardell, J.L.


Abstract

The ease of thermal cyclisation of 2-chloro-N-(R-2-pyridinyl)nicotinamides, (5: X = NH) to 5-oxo-5,6-dihydrodipyrido-[1,2-a:3‘,2‘-e]pyrimidin-11-ium chlorides in solution has been found to be in the order: (5: X = NH; R = 4-Me) > (5: X = NH; R = 5-Me) > (5: X = H; R = 6-Me) > (5: X =NH; R = 3-Me). This order reflects both steric and electronic effects of the methyl groups. The products of the cyclisations, which were monitored by NMR spectroscopy in DMSO-d6, were generally characterised by NMR spectroscopy and, specifically for 9-Me-5-oxo-5,6-dihydrodipyrido[1,2-a:3‘,2‘-e]pyrimidin-11-ium chloride, by X-ray crystallography. The crystal structure of 2-chloro-N-(6-methyl-2-pyridinyl)nicotinamide is also reported. The ester and thioester analogues, 2-pyridinyl 2-chloronicotinate and S-(2-pyridinyl) 2-chloro-3-pyridinecarbothioate, do not undergo cyclisation under the same conditions used for the amides.
Keywords: CYCLISATION, NICOTINAMIDES, FUSED PYRIDINES, FUSED PYRIMIDINES, 1,2-DIPYRIDINIUM SALTS Document Type: Research Article DOI: http://dx.doi.org/10.3184/030823406776331007 Publication date: 1 de Fevereiro de 2006

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