Identification of N‐ or O‐alkylation of aromatic nitrogen heterocycles and N‐oxides using 1H–15N HMBC NMR spectroscopy

dc.contributor.authorSheehy, Kevin J.
dc.contributor.authorBateman, Lorraine M.
dc.contributor.authorFlosbach, Niko T.
dc.contributor.authorBreugst, Martin
dc.contributor.authorByrne, Peter A.
dc.contributor.funderIrish Research Councilen
dc.date.accessioned2020-08-05T14:46:49Z
dc.date.available2020-08-05T14:46:49Z
dc.date.issued2020-06-09
dc.date.updated2020-08-04T01:00:28Z
dc.description.abstractA series of representative diazines and pyridine N‐oxides were subjected to alkylation using several different alkylating agents. The 15N NMR chemical shifts (δN values) of the diazines, pyridine N‐oxides and derived alkylation products were determined using 1H‐15N HMBC NMR spectroscopy at natural 15N abundance. The changes in the 15N NMR chemical shifts (Δ(δN) values) that occurred on going from starting materials to products in these reactions were analyzed. N‐alkylation of diazines resulted in large upfield shifts of the δN values of the alkylated nitrogen (of the order of 100 ppm or greater). While O‐alkylation of pyridine N‐oxides resulted in upfield shifts of the δN values of the N‐(alkoxy)pyridinium nitrogen, the Δ(δN) values were of a much smaller magnitude (ca . –42 ppm) than those observed for N‐alkylations of diazines. Nitrogen NMR spectroscopic data from the literature of relevance to alkylation of azines, diazines, azine N‐oxides and diazine N‐oxides was gathered together, and using this in tandem with our 15N NMR spectroscopic data, we have been able to corroborate our observations on the trends observed in the Δ(δN) values associated with N‐ and O‐alkylation reactions of aromatic N‐heterocycles and N‐oxides. An analysis protocol that relies on synergistic evaluation of 1H‐15N HMBC and 1H‐13C HMBC NMR spectra has been developed that enables unambiguous diagnosis of the occurrence of N‐alkylation of aromatic N‐heterocycles and O‐alkylation of aromatic N‐oxides.en
dc.description.sponsorshipIrish Research Council (Grant Number: IRC GOIPG/2018/1517)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationSheehy, K. J., Bateman, L. M., Flosbach, N. T., Breugst, M. and Byrne, P. A. (2020) 'Identification of N- or O-Alkylation of Aromatic Nitrogen Heterocycles and N-Oxides Using 1H–15N HMBC NMR Spectroscopy', European Journal of Organic Chemistry, 2020(22), pp. 3270-3281. doi: 10.1002/ejoc.202000329en
dc.identifier.doi10.1002/ejoc.202000329en
dc.identifier.eissn1099-0690
dc.identifier.endpage3281en
dc.identifier.issn1434-193X
dc.identifier.journaltitleEuropean Journal of Organic Chemistryen
dc.identifier.startpage3270en
dc.identifier.urihttps://hdl.handle.net/10468/10358
dc.identifier.volume22en
dc.language.isoenen
dc.publisherWileyen
dc.relation.urihttps://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/ejoc.202000329
dc.rights© 2020 The Authors. Published by Wiley‐VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.en
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en
dc.subjectAlkylationen
dc.subjectNitrogen heterocyclesen
dc.subject1H–15N HMBCen
dc.subjectNitrogenen
dc.subjectNMR spectroscopyen
dc.titleIdentification of N‐ or O‐alkylation of aromatic nitrogen heterocycles and N‐oxides using 1H–15N HMBC NMR spectroscopyen
dc.typeArticle (peer-reviewed)en
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