NMR Spectroscopy of Naturally Occurring Phloroglucinol Derivatives

Publisher Website
Google Scholar
Abstract
13C NMR spectra of eight 2-acyl- and -6-methyl-substituted filicinic acid (4,4-dimethyl-1,3,5-cyclohexantrione) derivatives were recorded in hexadeuterioacetone and in deuteriochloroform and the signals assigned on the basis of chemical shifts and CH coupling considerations. The prevailing tautomeric structure of these derivatives is the monoketonic one with the carbonyl function in position 3 and hydroxyl groups in positions 1 and 5, former, H-bonded to the acyl side chain carbonyl. The 2-acyl-6,6-dimethyl compounds have the diketonic structure and a H-bonded hydroxyl group in position 3. The skeletal structure of 2-butyryl-4-hydroxy-4,6-dimethyl-1,3,5-cyclohexantrione is identical with that of humulone. This compound and its homologs also exist in the monoketonic tautomeric form, where C-3 carries the carbonyl function. In the solvents used, the 6-methyl-2,3- dihydropyran-2,4-dione exists predominantly as a single tautomer having 2 ring double bonds; the remaining carbonyl group is a part of an .alpha., .beta.-unsaturated lactone grouping.