Isoquinoline methiodides react with phthalides in the presence of sodium methoxide to give intermediates which may be reduced to phthalide isoquinolines with hydrogen or sodium cyanoborohydride. The predominant isomer formed is the erythro, which is also the more active compound when tested for central nervous system activity. The direct coupling of phthalides with dihydroisoquinoline methiodides under these conditions fails to occur.