PURPOSE: To obtain the title compound, co-enzyme Q10, etc. useful as a drug for heart diseases, by oxidizing a condensate, prepared from a hydroquinone derivative and (iso)prenyl alcohol in the presence of a nitroalkane and a Lewis acid catalyst.

CONSTITUTION: A compound of formula I (R1 is H or lower alkyl group; R2 and R3 are lower alkoxy groups, or may form a naphthalene ring) is condensed with a compound of formula II or III (X is OH, halogen, acyloxy, or allylsulfonyloxy group; n is an integer 1W9) in the presence of a Lewis acid catalyst and a nitroalkane, e.g. nitromethane, etc. to form a compound of formula IV, which is oxidized to give the objective compound, e.g. vitamin K, Plastoquinone, or co-enzyme Q, of formula V. The method provides the product readily in a high yield commercially with suppressed side reactions without inhibiting the main reaction.