Direct observation of an adduct of 2-chlorotropone and potassium methoxide: attack at an unsubstituted cycloheptatrienone ring carbon

Abstract

It is shown by ¹H Fourier transform n.m.r. spectroscopy that potassium methoxide in dimethyl sulphoxide adds at C-7 of an activated cycloheptatrienone like 2-chlorotropone; this adduct rapidly disappears owing to competitive direct replacement of chlorine by methoxide from 2-chlorotropone present at equilibrium to give 2-methoxytropone which, finally, is trapped by methoxide as a gem-dimethoxy-adduct.