The ammonia-free partial reduction of substituted pyridinium salts

Organic & Biomolecular Chemistry
Timothy J DonohoeOsamu Ichihara

Abstract

This paper reports a study into the partial reduction of N-alkylpyridinium salts together with subsequent elaboration of the intermediates thus produced. Activation of a pyridinium salt by placing an ester group at C-2, allows the addition of two electrons to give a synthetically versatile enolate intermediate which can be trapped with a variety of electrophiles. Furthermore, the presence of a 4-methoxy substituent on the pyridine nucleus enhances the stability of the enolate reaction products, and hydrolysis in situ gives stable dihydropyridone derivatives in good yields. These versatile compounds are prepared in just three steps from picolinic acid and can be derivatised at any position on the ring, including nitrogen when a p-methoxybenzyl group is used as the N-activating group on the pyridinium salt. This publication describes our exploration of the optimum reducing conditions, the most appropriate N-alkyl protecting group, as well as the best position on the ring for the methoxy group. Electrochemical techniques which mimic the synthetic reducing conditions are utilised and they give clear support for our proposed mechanism of reduction in which there is a stepwise addition of two electrons to the heterocycle, mediated by...Continue Reading

References

Jan 22, 1975·Journal of the American Chemical Society·S DanishefskyA Nagel
Dec 2, 2000·Organic Letters·T J DonohoeP Sheldrake
Oct 25, 2001·The Journal of Organic Chemistry·Julie Fields Liu, Clayton H. Heathcock
Jul 6, 2002·The Journal of Organic Chemistry·Timothy J Donohoe, David House
Dec 3, 2003·Organic & Biomolecular Chemistry·Timothy J DonohoeK W Ace
Apr 13, 2004·The Journal of Organic Chemistry·Jeffrey T Kuethe, Daniel L Comins
Aug 4, 2004·The Journal of Organic Chemistry·Jeffrey T Kuethe, Daniel L Comins
Jun 18, 2005·The Journal of Organic Chemistry·Daniel L CominsClinton A Brooks

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Citations

Oct 12, 2010·The Journal of Organic Chemistry·Micah J NiphakisGunda I Georg
Oct 28, 2016·The Journal of Organic Chemistry·Richard R Hill, Scott D Rychnovsky
Apr 9, 2021·Angewandte Chemie·Arne HeuslerFrank Glorius
Jul 10, 2013·The Journal of Organic Chemistry·Khanh Hung NguyenNicolas Gouault
May 31, 2018·Organic Letters·Peng LeiJie An

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