Biogenetic-typetotalsynthesis of citromycetin (1a) was achieved by a route involving oxidation of a propenyl group and demethylation of a methoxy group in the pyranobenzopyranone (1c), synthesized by a regioselctive cyclization of the enedione (2c).
Biomimetic totalsynthesis of citromycetin (1a) is described. Regioselective cyclization of the enetrione (5), chosen as a common intermediate for the syntheses of citromycetin (1a) and fulvic acid (2a), with conc. HCI–AcOH (1:30) gave the chioromethylpyrone (7b). Oxidation, followed by demethylation of the substituents of the pyranobenzopyranone obtained by debenzylation and cyclization of the reactive