Abstract

AbstractThree groups of alkyl‐substituted naphthazarins were studied by 1H and 13C NMR in chloroform‐d at ambient temperature. Preliminary 1H NMR studies were carried out on selected members of each group at low temperatures (down to –120 °C) in dichloromethane‐d2 solution. Monoalkylnaphthazarins were found to exist predominantly as the 2‐alkyl tautomers (I) and the dimethylalkyl species as the 2,3‐dimethyl‐6‐alkyl tautomers (I). However, both symmetrically and unsymmetrically substituted 2,6‐ and 2,7‐dialkylnaphthazarins exhibited averaged chemical shifts and coupling constants indicating rapid proton exchange between the two minimum energy 1,4‐dione tautomers (I and II). 13C NMR shifts were utilized to calculate tautomer populations of the unsymmetrical 2,6‐ and 2,7‐(methyl,alkyl)naphthazarins.

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