Autoxidation study of carotane sesquiterpenes possessing a non-conjugated 1,4-diene system

The autoxidation process of carota-1,4-diene derivatives was studied. Several intermediate compounds in the autoxidation were isolated and characterized by spectroscopic methods, and two pathways, yielding 1,5-epidioxy-2-hydroperoxy derivatives and 1,5-epidioxy-14-norcarot-2-en-4-one, respectively, were confirmed. 5-Hydroperoxy-1,3-dienes undergoing spontaneous cyclization to yield 1,5-epidioxy derivatives were isolated as key intermediates in the first oxygen-addition step, whereas 1,5-epidioxy-4-hydroperoxy derivatives were identified as precursors of 1,5-epidioxy-14-norcarot-2-en-4-one. These observations supported a unique radical-mediated peroxidation process for carota-1,4-dienes.