4-OXOPENTADECANEDIOIC ACID IS PREPARED BY OXIDIZING A .alpha.-CYCLODODEC-1-ENYLPROPIONIC ACID DERIVATIVE HAVING ONE OF THE FOLLOWING CHEMICAL FORMULAE AT ITS ETHYLENIC DOUBLE BOND WITH OZONE. ##STR1## The compound is useful as an intermediate for a musk perfume compound. The compound having the formula II is selectively prepared from cyclododecanone and di-alkyl succinate.