The total synthesis of 4-formyl-3-hydroxy-8-methoxy-1,9-dimethyl-11-oxo-11H-dibenzo[b,e][1,4]dioxepin-6-carboxylic acid (psoromic acid)(28), a lichen depsidone, by selective functionalization of synthetic methyl 3,8-dimethozy-1,4,9-trimethyl-11-oxo-11H-dibbnzo[b,e][1,4]dioxepin-6-carboxylate (methyl O-methylhypopsoromate)(23) and subsequent steps, is described. Åttention is drawn to the use of isopropyl ethers as phenol protective groups.
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SALA et al. (1979) studied this question.