Iodination of 3,4,5-trimethoxybenzyl alcohol (I) with iodine in the presence of silver trifluoroacetate gave the 2-iodobenzyl alcohol (II). Subsequent palladium-catalyzed carbonylation-lactonization reaction with (II) gave rise to phthalide (III). This was brominated using NBS to afford the 3-bromophthalide (IV). Finally, condensation of (IV) with (1-naphthyl)methylphosphonic acid (V) yielded the title bisphthalidyl phosphonate.