The stereochemistry of quaternary N-methyl sparteinium cations, their derivatives, stereoisomers and analogues

An Isosparteine Derivative for Stereochemical Assignment of Stereogenic (Chiral) Methyl Groups Using Tritium NMR: Theory and Experiment

“…An optimized structure was computed for this molecule at the DFT/B3LYP/6-31G(d) level; in this structure, one of the methyl C−H bonds is directly oriented toward the opposing nitrogen lone pair. A full calculation of the vibrational modes for this structure gave no imaginary frequencies, nor any close to 0, indicating that the stationary point found by the optimization procedure was an energy minimum . A comparison of the computed vibrational modes that best reflect each localized methyl C−H stretching motion indicates that the bridging stretch is red-shifted relative to the other two methyl C−H stretches by 102 and 173 cm -1 .…”

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

“…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 .…”

“…The methodology for computing NMR parameters was based upon similar work in the literature . Crystal structures for 3 and 4 were retrieved from the Cambridge Crystallographic Database, and the cationic skeletons were used as starting structures for calculations. A 3‐step process was utilized to arrive at the computed shifts.…”

Indolizidine and quinolizidine alkaloids

“…ref. 26f), has now been published in fu11.1°2 Comins and co-workers have devised the highly stereoselective synthesis of epimyrtine (161) shown in Scheme 20.1°3 In the stereochemically important step, dihydropyridine (162) was reduced with triethylsilane and trifluoroacetic acid at -60 "C to give an 8 : 1 ratio of the 2,6-cisdisubstituted tetrahydropyridine (1 63) and its trans diastereomer. The yield of epimyrtine from 4-chloropyridine was 13.6 YO.…”