Exaltone ® (=Cyclopentadecanone) from Isomuscone ® (=Cyclohexadecanone), a One‐C‐Atom Ring‐Contraction Methodology via a Stereospecific Favorskii Rearrangement: Regioselective Application to (−)‐( R )‐Muscone

Treatment of cyclohexadecanone ( 1g ; with I 2 (2.2 mol‐euqiv.) and KOH in MeOH) furnished the unsaturated ( Z )‐ester 2g in 83% yield, via a stereospecific Favorskii rearrangement ( Scheme 1 ). Further treatment with 3‐chloroperbenzoic acid ( m ‐CPBA) afforded the unreported epoxy ester 3g (88% yield), which was cleaved in 33% yield to Exaltone ® (=cyclopentadecanone; 1f ) with NaOH in MeOH/H 2 O and then HCl at 65°. This methodology was similarly extended to higher (C 17 ) and lower (C 15 to C 11 ) cyclic ketone analogues, as well as regioselectively to (−)‐( R )‐muscone ( 5c ) and homomuscone ( 5f ) ( Scheme 2 ). Olfactive properties of the corresponding macrocyclic 1‐oxaspiro[2, n ]alkanes and ‐alkenes 4 and 8 , resulting from a Corey Chaykovsky oxiranylation, are also presented.