To obtain a catalyst system having no corrosiveness or poisonousness, not polluting the environment and capable of exhibiting catalystic action on the objective reaction with high selectivity and a high yield by using a protonic acid catalyst for a condensation reaction contg. a specified bis(oxalato)borate.

Friedel-Crafts condensation reaction, the condensation reaction of vinyl ether or the acylation reaction of phenol is carried out as a condensation reaction in the presence of about 0.1-6mol% bis(oxalato)borate represented by the formula as a catalyst at about 0-140°C temp. dependent on the kind of starting material in the presence or absence of a solvent. In such a condensation reaction, 4-hydroxy-2-methylnaphthalen-1-yl benzoate or trimethylhydroquinone is preferably allowed to react with isophytol.