2,6,6-Trimethylcyclohepta-2,4-dienone and 3,6,6-trimethylcyclohepta-2,4-dienone ? Components of the turpentine from Pinus sylvestris

Skeletal rearrangements of monoterpenoids of the carane series

“…61,62 It was then found that rearrangements of carane derivatives into trimethylcycloheptane ones are much more common, because the equilibrium in the dynamic interconversion of the two tautomers is strongly shifted toward the monocyclic partner. 63 2,5,5-Trimethylcyclohepta-2,4-dienone (67), like the ketone 62, has been found in the turpentines obtained from Pinus silvestris L. 64 Probably, the presence of these ketones in turpentine oil is explained by the formation, during plant growth, of caranetype unsaturated ketones from 3-carene (one of the major turpentine components); these are then transformed into monocyclic dienones in a concerted electrocyclic reaction. This is supported by the results of liquid-phase oxidation of 3-carene: the percentage of ketones 62 and 67 in the reaction products was 20% and 28%, respectively.…”