合成路线1

The metal-ammonia reduction of 4,6-dimethoxy-m-xylene (I) gives 1,5-dimethyl-2,4-dimethoxy-1,4-cyclohexadiene (II), which by treatment with potassium tert-butoxide in DMSO is converted into the conjugated diene (III). The Dies-Alder reaction of (III) with dimethyl acetylenedicarboxylate (A), and subsequent elimination of the bridge affords dimethyl 3-methyl-4,6-dimethoxyphthalate (IV), which is selectively monodemethylated with BCl3 yielding the o-hydroxyphthalic ester (V). The hydrolysis and anhydrization of (V) gives 3-hydroxy-5-methoxy-6-methylphthalic anhydride (VI), which is reduced with Zn and HCl in acetic acid affording 4-methyl-5-methoxy-7-hydroxyphthalide (VII). The reaction of (VII) with allyl bromide (B) by means of K2CO3 in ether gives the allylic ether (VIII), which undergoes thermal rearrangement into 4-methyl-5-methoxy-7-hydroxy-6-allyl-phthalide (IX). The ozonolysis of (IX) affords the aldehyde (X), which by a Wittig condensation with 1-formylethylydenetriphenylphosphorane (XI) is converted into the new aldehyde (XII). A new Wittig reaction of (XII) with the phosphorane (XIII) gives the ethyl ester (XIV), which is finally hydrolyzed and partially reduced with diimide.