Spectral assignments and structural studies of a warfarin derivative stereoselectively formed by tandem cyclization

• Stereoselective synthesis of a coumarin as well as piperidine based derivative.
• Simple one–pot tandem process involving Mannich and enamine reactions.
• Structure elucidation through 1–D and 2–D NMR spectra in the solution state.
• Comparison of single crystal and theoretically derived data for discussion.

The structural elucidation of a Mannich condensation product of rac–Warfarin with benzaldehyde and methyl amine was carried out using IR, Mass, 1H NMR, 13C NMR, 1H–1H COSY, 1H–13C COSY, DEPT–135, HMBC, NOESY spectra and single crystal X-ray diffraction. Formation of a new pyran ring via a tandem cyclization in the presence of methyl amine was observed. The optimized geometry and HOMO–LUMO energy gap along with other important physical parameters were found by Gaussian 09 program using HF 6–31G (d, p) and B3YLP/DFT 6–31G (d, p) level of theory. The preferred conformation of the piperidine ring in solution state was found to be chair from the NMR spectra. Single crystal X-ray diffraction and optimized geometry (by theoretical study) also confirms the chair conformation in the solid state.

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