To produce the subject compound in high yield without causing corrosive actions, etc., with a catalyst by condensing timethylhydroquinone with isophytol in the presence of a specific amine catalyst in supercritical carbon dioxide or supercritical nitrous oxide.

(A) Trimethylhydroquinone is condensed with (B) isophytol in the presence of (D) bis-(trifluoromethylsulfonyl)amine or a metal salt represented by the formula [Met is boron, magnesium, aluminum or the like; (n) is the corresponding valence of the metal atom Met and 1-4] as a catalyst in (C) supercritical carbon dioxide or supercritical nitrous oxide to thereby produce the objective compound. The molar ratio of the component A to the component B is preferably (0.8:1) to (1.2:1). The amount of the component D used is preferably (1:1,000) to (1:10O) based on the component A or B expressed in terms of molar ratio. The amount of the component C used is preferably (2:1) to (8:1) based on the component A or B expressed in terms of weight ratio.