The invention discloses a new synthesizing method of 3-methyl-7, 8-dihydroxy isochroman ketone-4, which comprises the following steps: adopting 2, 3-dimethoxy benzenemethanol as raw material; bromodizing; obtaining 6-bromine-2, 3-dimethoxy benzenemethanol to etherify with 2-bromopropionic ether; obtaining 2-(6-bromine-2, 3-dimethoxy benzyloxy) propionic ether; hydrolyzing to produce 2-(6-bromine-2, 3-dimethoxy benzyloxy) propanoic acid; proceeding nucleophilic additional reaction under organic lithium agent; obtaining 3-methyl-7, 8-dimethoxy isochroman ketone-4; demethylating to obtain 3-methyl-7, 8-dihydroxy isochroman ketone-4. |