Muscone (3-methylcyclopentadecanone) is a major macrocyclic ketone found in the solid secretion, commonly known as musk, from the pouch ofMoschus moschiferus. Herein, we report its synthesis from 10-undecenoic acid, which is the major product of castor oil pyrolysis. Methyl 14-oxotetradecanoate was prepared by radical addition of methyl 10-undecenoate to acrolein. The terminal oxo group was protected as an acetal, and the ester group was treated with the anion of dimethyl methylphosphonate (CH3-(O)P(OMe)2, DMMP) to give 2-(15-dimethoxyphosphynil-14-oxo-pentadecane)-1,3-dioxolane. The acetal protection was removed and the Emmons-Horner reaction was carried out in K2CO3-t-butanol to give 2-cyclopenta-decenone. The addition of MeMgI in the presence of Cu2Cl2gave muscone.