13C NMR study on linderones and lucidones

Abstract
The 13C NMR spectra of linderone (1), lucidone (2), methyllinderone (3), methyllucidone (4), demethyllinderone (7), dihydrolinderone (8) and 2‐(1‐hydroxyethylidene)‐4‐methylcyclopent‐4‐ene‐1,3‐dione (9) are reported. The 1H chemical shift data for 1–4 are also reported. Geometric isomers exist in 4, while external tautomers exist in all the other compounds (except 3) through strong intramolecular hydrogen bonding. With the aid of deuterium isotope effects (in 1 and 2), C‐H coupling constants and nuclear Overhauser effects, the 13C NMR spectra are assigned to the external tautomers and the geometric isomers.