¹⁷O NMR studies on polycyclic quinones, hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators

Abstract

Abstract The 17 O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex‐2‐enone (1), α‐tetralone (2), anthrone (3), 4 H ‐pyran‐4‐one (4), 1‐benzopyran‐4(4 H )‐one (5), xanth‐9‐enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5‐dihydroxybenzoquinone 5,8‐dihydroxynaphthoquinone and 1,4‐dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused‐ring effect on the carbonyl chemical shift. A single 17 O resonance was observed for 2,5‐dihydroxybenzoquinone (358 ppm) and 5,8‐dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4‐dihydroxyanthraquinone gave two discrete 17 O signals at 441 and 87 ppm, indicating that in this case proton exchange between oxygen atoms is slow.