Studies on the Oxidation of cis- and trans-Pinane with Molecular Oxygen

Article abstract of DOI:10.1002/prac.19923340506

The pinanes are preferably attacked at the tertiary C-H bond in 2-position, but products of the oxidative attack at the secondary C-H-bonds in 3- and 4-position are also found.At 100 deg C cis-pinane is attacked more easily than trans-pinane (k_cis : k_trans = 6.4), the relative rates of attack at the secondary C-H bonds in positions 3 and 4 with respect to the tertiary C-H bond in 2-position were also determined (in cis-pinane k_sec : k_tert = 0.027; in trans-pinane k_sec : k_tert = 0.20).After the attack at the 2-C-H bond the radical formed can either react with oxygen to form the corresponding cis- and trans-peroxy radicals and further to give cis- and trans-2-hydroperoxy pinane or fragmentate to the monocyclic radical derived from α-terpinene, giving as a final products α-terpinene hydroperoxide and the bicyclic 8-hydroperoxy 4,4,8-trimethyl 2,3-dioxabicyclo<3.3.1>nonane.The corresponding alcohols were found after reduction with sodium sulphite.The oxidation at position 2 of the pinanes delivers not only the cis- and trans-hydroperoxide but also, as short-lived intermediates, the corresponding 2-pinanyloxy radicals.These radicals fragmentate forming a carbon radical with cyclobutane structure whose oxidation products were identified.Besides fragmentation of the 2-pinanyloxy radical also an intramolecular H-transfer from the methyl group in 9-position to the oxygen of the trans-pinanyloxy radical takes place leading to 9-hydroperoxy trans-pinane-2-ol.