Nuclear magnetic resonance studies. V. The tautomerism of tasmanone and related β-triketones

Abstract

From a nuclear magnetic resonance study of the tautomerism of tasmanone and 1,1,3,3-tetramethylphloroglucinol (syncarpic acid), it is deduced that tasmanone consists of a mixture of tautomers (I) and (II) with the tautomer (I) present in the larger proportion. Similarly it is deduced that the tautomers of agglomerone (XI; R = CHMe2), 3-acetyl-O-methylfilicinic acid (XI R; = Me), ceroptene (XI; R = CH=CHPh), and usnic acid (XIII) with the extended conjugation are the more stable and populated ones.