An Intramolecular Enyne Metathesis Approach for the Synthesis of Cyclic 3‐Substituted Unsaturated Sulfones

Studies into the ring‐closing enyne metathesis of a series of nine sulfone containing enynes is described. The readily accessible sulfone substrates were shown to undergo cyclisation to form 3‐subsituted 2,5‐dihydrothiophene 1,1‐dioxides (sulfolenes) and one 3,6‐dihydro‐2H‐thiopyran 1,1‐dioxide. The success of this process depended on the substrate's substitution pattern. Moderate to good yields of the products were obtained when the ene component was monosubstituted and it was found that the reactions proceeded most efficiently using the 2nd generation Grubbs catalysts, at elevated temperatures. A ring closing enyne metathesis for the synthesis of a series of unsaturated cyclic sulfones is described. The reaction proceeds most effectively with the N‐heterocyclic ruthenium carbene catalysts and the rate of reaction depends on the identity of the alkynyl substituent.