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

Abstract

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.