Disclosed is a process for efficiently producing a compound represented by formula (I): ##STR00001## wherein R.sup.1 represents aryl, amino, alkyl, or alkoxy; R.sup.2 represents a protective group of the carboxylic acid; and R.sup.3 represents an alkali metal, a hydrogen atom, alkyl, aryl, alkylsulfonyl, arylsulfonyl, or trialkylsilyl. This process is characterized by reacting a compound of formula (II) with a compound of formula (III) in the presence of a transition metal compound. ##STR00002##