Transformation of the pheromone 3-methyl-2-cyclohexen-1-ol in the presence of [RuClCp (PTA)₂] and [RuCp (OH₂)(PTA)₂]CF₃SO₃

The catalytic conversion of the substituted cyclic allylic alcohol 3-methyl-2-cyclohexen-1-ol was studied in the presence of the metal complexes [RuClCp (PTA)(2)] (1) and [RuCp (OH2)(PTA)(2)]CF3SO3 (2) (PTA = 1,3,5-triaza-7-phosphaadamantane) in different media such as water, methanol, and biphasic water/cyclohexane. Slight changes of the reaction conditions led to the isomerization to 3-methylcyclohexanone, oxidation to 3-methyl-2-cyclohexenone, or 1,3-transposition to 1-methyl-2-cyclohexen-1-ol. The 1,3-transposition and oxidation reactions took place in water, and the selective formation of the isomerization product was achieved in freshly dried methanol, or biphasic water/cyclohexane mixture, achieving the highest TON values known to date. Furthermore, the reactivity of 3-methyl-2-cyclohexen-1-ol in water was also investigated in the absence of a catalyst, revealing the formation of the 1,3-transpostion product 1-methyl-2-cyclohexen-1-ol and the etherification product 1-methyl-3-(3-methyl-2-cyclohexen-1-yl)oxycyclohexene. Finally, key mechanistic aspects of the different reaction pathways were enlightened by NMR spectroscopy.