To obtain in high optical yield the subject compound as a raw material compound for optically active forms of ketene S,S-acetals useful as antimycotic agents by reduction of an acetophenone derivative in the presence of a catalyst consisting of a complex of bisorganophosphorus-based compound and rhodium.

(C) This compound of formula IV (e.g. a compound of formula V) is obtained by reducing (A) a compound of formula I (R1 is H, halogen or the like; R2 is H, a 1-6C alkyl or the like; and (n) is 1-5) (e.g. 2,2',4'- trichloroacetophenone) in the presence of (B) a catalyst of formula II (R is a 1-6C alkyl, 3-8C cycloalkyl or 1-adamantyl group; and (n) is 1 or 2) (e.g. a compound of formula III) using a reducing agent such as ethylsilane or methylphenylsilane, pref. at -80 to room temperature; wherein the amount of the component B to be used is pref. 0.1-0.0001 wt.% based on the component A.