Ring closing alkyne metathesis: stereoselective synthesis of civetone

A concise and stereoselective synthesis of the macrocyclic musk civetone 6 is reported starting from readily available 9-undecynol. The key steps comprise a ring closing metathesis of diyne 4 followed by Lindlar reduction of the resulting cycloalkyne 5. The cyclization can be effected either by using catalytic amounts of the Schrock alkylidyne complex (t-BuO)3WCCMe3 or by means of an in situ catalyst mixture generated from Mo(CO)6 and p-trifluoromethylphenol. Both catalyst systems turned out to be compatible with the unprotected ketone function of the substrate.