N-Methylation of methyl 5-hydroxynicotinate followed by reaction with a diene in the presence of triethylamine afforded (4+3) cycloadducts in good to excellent yields. High regioselectivity was observed with 1-substituted and 1,2-disubstituted butadienes. Density functional theory calculations indicate that the cycloaddition involves concerted addition of the diene onto the oxidopyridinium ion. The process provides rapid access to bicyclic nitrogenous structures resembling natural alkaloids.
Keywords: (4+3) cycloaddition; alkaloids; dienes; pyridinium ions.
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.