PURPOSE: To obtain the titled compound in good yield, by converting 3- methoxy-5-bromocatechol as a raw material into a methylenedioxy derivative using a dihalomethane, reacting the resultant derivative with metallic Mg to form a Grignard reagent and reacting the resultant reagent with paraformaldehyde.

CONSTITUTION: 3-Methoxy-5-bromocatechol expressed by formula I is converted into methylenedioxy derivative in the presence of a deacidifying agent, e.g. anhydrous K2CO3, in an aprotic solvent, e.g. N,N-dimethylformamide, at 0W200°C using a dihalomethane, e.g. methylene chloride, to form 3-methoxy-4,5- methylenedioxybromobenzene expressed by formula II, which is then reacted with metallic Mg in a polar solvent, e.g. anhydrous tetrahydrofuran, at -20W+150°C to give a Grignard reagent. The resultant Grignard reagent is then reacted with paraformaldehyde at -10W+150°C to afford the aimed 3,4- methylenedioxy-5-methoxy-benzyl alcohol expressed by formula III.

USE: An intermediate raw material for medicines, etc.