Selective protection of catechin gives access to the intrinsic reactivity of the two phenol rings during H-abstraction and photo-oxidation

Selective protection of the catechol ring of catechin has been achieved. From this key compound, catechin analogues protected either on the catechol or the resorcinol rings were synthesized. From these analogues, phenoxyl radicals on the catechol or on the resorcinol rings were produced by photo-oxidation (direct irradiation at 308 nm) of the phenolate and by H-abstraction experiments. Spectra of the radicals were recorded at short times before any further chemical evolution. Investigation of catechin behavior itself and comparison with the reactivity of models show that H-abstraction is unselective, whereas photooxidation is selective on the catechol ring monoanion establishing that this ring has the lowest pKa. (C) 2000 Elsevier Science Ltd. All rights reserved.