EVIDENCE FOR THE EXISTENCE OF A CYCLIC RUTHENIUM(VI) DIESTER AS AN INTERMEDIATE IN THE OXIDATIVE SCISSION OF (-)-ALPHA-PINENE WITH RUO4

The reaction of(-)-alpha-pinene (1) with RuO4 in CCl4 at room temperat ure affords the ketoaldehyde 3 as the sole product. Evidence is report ed that the oxidative scission of the olefinic substrate to 3 proceeds through a ruthenium (VI) diester intermediate for which we propose st ructure 2 on the basis of spectral evidence and comparison with the os mium-containing analogue of 2, synthesised by reaction of(-)alpha-pine ne with OsO4 in dioxane and whose structure has been determinated by s ingle crystal X-ray diffraction analysis. Compound 2 was also shown to be an intermediate compound in the RuO4 oxidation of (-)-alpha-pinene performed in acetone-water (2:1) which gives alpha-ketol 4 as the sol e oxidation product.