Process for the preparation of novel unsaturated macrocyclic ketones

A process for the preparation of macrocyclic ketones of formula ##STR16## wherein R.sup.1 represents a lower alkyl radical or a hydrogen atom, which comprises

• a. reacting in the presence of a basic reagent a dialdehyde of formula ##STR17## possessing two single or two double bonds in the positions indicated by the dotted lines and wherein index n stands for integer 1 or 2, with a diphosphonate of formula ##STR18## wherein each of symbols R represents an alkyl radical, to give an unsaturated macrocyclic ketone of formula ##STR19## b. catalytically hydrogenating the thus obtained ketone to give cyclopentadecanone, or
• c. alkylating the ketone of formula (I) obtained in step a. in order to obtain the compound of formula ##STR20## wherein R.sup.1 represents a lower alkyl radical and index n stands for integer 1 or 2, and
• d. catalytically hydrogenating compound (V) to give an alkylated macrocyclic ketone of formula ##STR21## wherein R.sup.1 has the meaning given for formula (V).