The cyclization of floroglucinol (I) with ethyl 2-oxohexanoate (II) in acidic medium gives 5,7-dihydroxy-4-propyl-2H-1-benzopyran-2-one (III), which is submitted to a Friedel Crafts condensation with propionyl chloride (IV) / AlCl3 to yield the 8-propionyl derivative (V). Finally, the cyclization of (V) with 3-hydroxy-3-methylbutyraldehyde dimethyl acetal (VI) in refluxing pyridine affords the target compound.