Loss of the acetyl group occurs when 2-acetyl-1,4-naphthoquinone epoxide (I; R = H) is treated with hydrogen bromide in acetic acid, whereas the acetyl group in the 3-methyl homologue (I; R = Me) is retained under these conditions. However it is the acetyl group in the latter epoxide only which is lost when the compounds are reduced by catalytic hydrogenation. C→O-Acetyl migration occurs when 2-acetyl-r-2,3-epoxy-3;4-dihydro-c-4-hydroxynaphthalen-1 (2H)-one (II; R = H) is treated with anhydrous magnesium bromide, and loss or C→O migration of the acetyl group is observed when 2-acetyl-t-3-bromo-2,3-dihydro-r-2-hydroxy-3-methyl-1,4-naphthoquinone (III; R = Me) is catalytically reduced. 3-Acetyl-3,4-dihydro-t-3,c-4-dihydroxy-r-2-methylnaphthalen-1 (2H)-one (IX; R = Me), which is also formed in the latter reaction, undergoes a major conformational change on transferring from dimethyl sulphoxide to chloroform solution. The stereospecific formation of this compound and its lower homologue and the behaviour of compounds (I; R = H),(I; R = Me), and (III; R = Me) under conditions of catalytic reduction are interpreted in terms of competing processes at substrate–catalyst complexes.