Synthesis of 4,6-dihydroxyisophthalaldehyde and the 5-methyl and 5-methoxy-derivatives

4,6-Dibromoresorcinol dimethyl ether has been converted into 4,6-dihydroxyisophthalaldehyde (11) by lithium–bromine interchange, formylation, and demethylation. Similarly the 5-methyl and 5-methoxy-derivatives were prepared, all in good overall yields. Three dioxa-anthracenediones have been prepared from the isophthalaldehydes. Low-temperature lithium–bromine interchange, formylation, and selective demethylation provided a route to 5-bromo-3,4-dimethoxysalicylaldehyde (14), which has potential as an intermediate for the synthesis of oxygen heterocycles.