ChemInform Abstract: Tetracyclic Alkaloids of the Sparteine Group. 1H and 13C NMR Spectroscopy and Conformational Analysis.

Abstract

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1H and 13C NMR assignments for (N‐Methyl)‐(−)‐(α)‐isosparteinium iodide and (N‐Methyl)‐(−)‐sparteinium iodide

“…Duddeck and coworkers reported 1 H chemical shifts (but not coupling constants) and 13 C chemical shifts for ( N ‐Methyl)‐(−)‐sparteinium iodide 3 alongside 10 other sparteine derivatives in 1995 . Their assignments, which were reported using a different skeletal numbering system, have been converted to the atom numbering system shown in Figure and are listed alongside those of ours in Tables and .…”

“…This study is focused on assigning 1 H chemical shifts and coupling constants and 13 C chemical shifts for N ‐Methyl derivatives of sparteine and isosparteine, both of which have been fully characterized by X‐ray crystallography. X‐ray analysis of ( N ‐Methyl)‐(−)‐sparteinium iodide ( 3 ) revealed a chair‐chair‐boat‐chair conformation (Figure ), and its 1 H and 13 C NMR chemical shift assignments were reported by Duddeck and coworkers in 1995 . An X‐ray analysis of ( N ‐Methyl)‐(α)‐isosparteinium iodide ( 4 ) showed an all‐chair conformation in which the N‐CH 3 group is positioned in close proximity to the transannular nitrogen lone pair, resulting in a + NCH•••N hydrogen bond .…”