(2+4)-cycloaddition with singlet oxygen. O-17-investigation of the reactivity of furfuryl alcohol endoperoxide

In earlier work, the use of furfuryl alcohol as a specific singlet oxygen a cceptor was proposed because of the high ratio between the rate constants o f chemical reaction and physical quenching. In contrast to furfuryl aldehyd e, a number of products are formed by this type II photooxidation of furfur yl alcohol. These products may be derived from the endoperoxide of furfuryl alcohol as a common intermediate. The present work focuses on the reactivi ty of this endoperoxide that was marked specifically by the use of O-17(2) as a source for singlet oxygen, The analyses of the stable products, their yields and their labeling distribution reveal a strong solvent effect on th e primary reaction pathways, and nucleophilic substitution reactions leadin g to hydroperoxide intermediates are dominant.