Deprotonation/Alkylation Reactions of Sulfolenes

Deprotonation/methylation reactions have been carried out on a series of substituted 2-sulfolenes and 3-sulfolenes. For 2-sulfolenes, both allylic and vinylic deprotonation reactions occur to give, after treatment with methyl iodide, 2-methylated 3-sulfolenes and 2-methylated 2-sulfolenes. These products are useful intermediates because substituted 3-sulfolenes are precursors to substituted butadienes and 2-alkylated 2-sulfolenes are precursors to β-functionalized trans olefins.     

Synthesis of Substituted 1,3‐Diene Synthetic Equivalents by a Ru‐Catalyzed Diyne Hydrative Cyclization

Catalyzed by [CpRu(CH₃CN)₃]PF₆, the hydrative cyclization of dipropargylic sulfone substrates provides an effective way to synthesize highly functionalized substituted 3‐sulfolenes. The amount of water is crucial for the reactivity of this cycloisomerization reaction. The scope and limitations of the Ru‐catalyzed cycloisomerization are discussed. A marked ketone‐directing effect was observed for the first time in ruthenium‐catalyzed cyclizations. A plausible mechanism for the ketone‐directed cycloisomerization is also rationalized. The utility of this method was demonstrated by both sulfur dioxide extrusion of the 3‐sulfolenes to afford 1,3‐dienes and subsequent inter‐ or intramolecular Diels–Alder reactions.