Efficient Synthesis and Anti-Tubercular Activity of a Series of Spirocycles: An Exercise in Open Science
Figure 7
The piperidine nitrogen signals of the acylated products can be visualised by HSQC experiments.
The 1H-NMR and 13C{1H}-NMR spectra respectively displayed on the x- and y-axes of the HSQC spectra are projections of the corresponding one-dimensional NMR experiments and are displayed for clarity. (A) The aliphatic region of the 1H–13C{1H} HSQC spectrum of 16; the red arrows indicate the 1H signals corresponding to the piperidine protons (attached to the red ring of the structure). The corresponding piperidine carbon signals on the y-axis (circled red) are unclear in the 13C{1H} spectrum. (B) Rotation around the amide bond generates chiral rotamers (C and D) dictated by the π-system of the benzamide, which makes the methylene protons in the oxygen-containing ring diastereotopic, (E) Variable magnetic field temperature and NMR experiments showing coalescence of methylene signals for compound 16. At lower temperature the diastereotopic oxygen-containing ring protons (E) exhibited higher order coupling, arising from the individual rotamers (Figure S39) and the 13C{1H} NMR spectrum exhibited complete resolution of the piperidine ring carbon signals (Figure S40). Raw data may be found in Dataset S1.