LAUSR

(−)‐Sparteine (1) and (−)‐(α)‐isosparteine (2) are members of the lupine alkaloid family. Sparteine has found extensive use in asymmetric organic transformations, including lithiations and Pd‐catalyzed oxidations. (α)‐Isosparteine, which can be made from sparteine, has been utilized as a chiral ligand for a limited number of stereoselective reactions. The two compounds differ in that 1 displays an exo–endo arrangement of the bridgehead hydrogens at C‐11 and C‐6, respectively, while 2 retains an exo–exo arrangement of these atoms (Figure 1). This study is focused on assigning H chemical shifts and coupling constants and 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 1), and its H and 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‐CH3 group is positioned in close proximity to the transannular nitrogen lone pair, resulting in a NCH•••N hydrogen bond. Our group has harnessed the bridging geometry in 4 with an equilibrium isotope effect to investigate H and H chemical shift differences in (N‐CH2D) and (N‐CHDT) isotopologs. Simeonov, Duddeck, and coworkers have previously reported H and C NMR chemical shift assignments for 4 dissolved in DMSO‐d6. [16] We noticed discrepancies between our H and C assignments for 3 and 4 and values reported in the earlier studies. This was especially true for the H data for 4, where 16 out of 27 assignments differ from the previously reported values. Spectral assignments for 3 and 4 are also compared with quantum‐mechanically computed C and H NMR chemical shifts to further validate the assignments reported here.