Performic acid oxidation of exo-2-syn-7-bicyclo[2.2.1]hept-5-enediol. H-1 and C-13 NMR spectroscopic structure elucidation of the reaction products

Performic acid oxidation of exo-2-syn-7-bicyclo[2.2.1]hept-5-enediol (norborn-5-enediol) gives exo-3-exo-5-syn-7-tricyclo[2.2.1.0(2,6)]heptanetriol-(nortricyclenetriol), exo-2-endo-3-endo-5-syn-7-, exo-2-endo-3-endo5-anti-7- and exo-2-endo-3-exo-5-anti-7-bicyclo[2.2.1]heptanetetrols (norbornanetetrols) as reaction products, the relative amounts being 13.7%, 48.1%, 20.2% and 10.4% respectively. The structures of these polyols were elucidated using H-1 and C-13 NMR spectroscopy including 2D H-1-H-1 NOESY, H-1-H-1 COSY, C-13-H-1 COSY and C-13-C-13 INADEQUATE spectra. The reaction mechanism, which consists first of the formation of a norbornyl cation gives, after deprotonation, a triol as an end product. The mechanism leading to the three tetrols includes (1) a Wagner-Meerwein (W-M) rearrangement, (2) a 6,2-hydride shift, (3) another W-M rearrangement and (4) exo attack of the formate anion. The mechanism has been described using the known classical carbocation intermediates. The absence of three theoretically possible reaction products can be explained by intermediates, where the attack of the formate anion on a carbocation is hindered by the vicinal exo hydroxyl group.