Muscone

Muscone (3-methylcyclopentadecanone, CAS 541-91-3) is the principal odorant of natural musk — the dried glandular secretion of the male musk deer (Moschus moschiferus). Heinrich Walbaum isolated it in 1906. Twenty years later, Leopold Ruzicka determined its structure: a 15-membered carbon ring bearing a methyl group and a ketone. Rings that large had been considered impossible under Baeyer's strain theory. Ruzicka proved otherwise, and the work contributed to his 1939 Nobel Prize in Chemistry.

Natural musk was harvested by killing the male deer and excising the glandular pod. Each pod yields roughly 15–25 grams of musk grain. Three to five deer die per pod recovered, because indiscriminate trapping kills females and juveniles too. All Moschus species are now listed on CITES Appendix I and classified as endangered or vulnerable on the IUCN Red List. No natural musk enters legitimate perfumery today.

Modern muscone is fully synthetic. The most restrained route starts from (+)-citronellal, proceeds through an acyclic diolefinic intermediate, and closes the macrocycle via olefin metathesis using a ruthenium benzylidene catalyst — yielding the cyclic precursor in approximately 78% yield, which is then hydrogenated to (R)-(−)-muscone. The (R)-enantiomer (l-muscone) is the more potent form: it activates the human musk receptor OR5AN1 with roughly three times the response intensity of the (S)-enantiomer, and its odor detection threshold sits at approximately 4.5 ng/L of air.

Muscone belongs to the macrocyclic musk class alongside civetone (C₁₇, from civet), exaltone (cyclopentadecanone, the unmethylated C₁₅ analogue), and ambrettolide (from ambrette seed). These large-ring molecules are prized over polycyclic and nitro musks for their superior olfactory quality, better biodegradability, and lower bioaccumulation risk.

Related notes: Amber · Ambergris · Ambrette · Ambroxan · Cashmeran · Cashmere · Ethylene Brassylate · Galaxolide