Pyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans

A thorough investigation of the minor oxidation products of two penta-tetrahydrofuran compounds with pyridinium chlorochromate has been carried out. Isolation of ring-B oxygenated spiroketal and degradation products, including polycyclic mono- and bis-lactone compounds, supports the previously postulated involvement of cyclic enolether intermediates in the oxidation of THF and poly-THF substances with PCC. Based on the collected evidence, a new mechanistic route for the PCC-mediated oxidative cleavage of α-hydroxy-THF compounds to γ-lactones has been postulated. The proposed mechanism well agrees with the one reported for the oxidative cleavage of 8-hydroxy-neoisocedranol oxide by RuO4, a fact that further supports our previous observation on the similar oxidizing behaviour shown by PPC and RuO4 towards THFcontaining compounds.