Résumé dans la langue de publication, traduction non disponible A process for producing a compound of the formula (I): wherein R**1 and R**2 are the same or different and are hydrogen or alkyl, and R is hydrogen or alkyl, which comprises removing the protective group (P) of hydroxyl of a compound of the formula (II): wherein is a protective group of hydroxyl, ∼ indicates an E-isomer, Z-isomer or a mixture thereof, and the other symbols are as defined above; and an intermediate for the production of the compound of the formula (I).