Studies on the syntheses of heterocyclic compounds containing benzopyrone. Part 5. Total synthesis of fulvic acid

Total synthesis of fulvic acid (1a) is described. Regioselective cyclization of the enedione (8f), an equivalent of the proposed biogenetic intermediate (5a) for citromycetin (2), gave the pyrone (11a), which led to fulvic acid (1a) by a route involving debenzylation, selective ozonization, and hydration.