The effect of fluorine on the diastereoselectivity of the addition of alpha-oxyradicals to 3-fluoro-2,3-dihydro-1H-lambda(6)-thiophene-1,1-dione

alpha-Oxyradicals generated from alcohols and ethers underwent addition to the vinyl sulfone 3-fluoro-2,3-dihydro-1H-lambda(6)-thiophene-1,1-dione (1) giving a new family of fluorinated compounds. The stereochemistry of the a ddition products 3-8 was confirmed by using both F-19 NMR spectroscopy and X-ray crystallography. In all cases, trans-isomers were preferentially form ed. The pi-facial stereoselection fails to follow the hyperconjugative theo ry of Cieplak, instead other possible explanations have been proposed under lying the importance of electronic contributions to the observed diastereos electivity. An additional vinyl sulfone 2-bromo-4-fluoro-4,5-dihydro-1H-lam bda(6)-thiophene-1,1-dione (10) was prepared via the successive bromination and dehydobromination of 1; its addition reaction with 2-propanol was also studied. (C) 1999 Elsevier Science S.A. All rights reserved.