Preparation of (E)‐4‐Aryl‐1,1,1‐trifluoro‐3‐tosylbut‐3‐en‐2‐ones as Fluorinated Building Blocks and Their Application in Ready and Highly Stereoselective Routes to trans‐2,3‐Dihydrofurans Substituted with Trifluoromethyl and Sulfonyl Groups

Abstract ( E )‐4‐Aryl‐1,1,1‐trifluoro‐3‐tosylbut‐3‐en‐2‐one fluorinated building blocks were prepared through a two‐step process. Treatment of these ( E )‐4‐aryl‐1,1,1‐trifluoro‐3‐tosylbut‐3‐en‐2‐ones with arsonium bromides in the presence of Cs 2 CO 3 in CH 2 Cl 2 at reflux resulted in highly stereoselective ring closure to provide 4‐tosyl‐5‐trifluoromethyl‐ trans ‐2,3‐dihydrofurans in good to excellent yields.