High 1,2-Asymmetric Induction in Radical Reactions: Radical Addition to γ-Hydroxy α,β-Unsaturated Carboxylic Esters and Sulfones

Article abstract of DOI:10.1246/bcsj.70.3091

High 1,2-asymmetric induction was realized by the addition of a 1-hydroxy-1 -methylethyl radical to conformationally flexible (E)-γ-hydroxy α,β-unsaturated carboxylic esters and sulfones (1 and 2, respectively). Upon the irradiation (> 290 nm) of (E)-1 and benzophenone in 2-propanol, the 1-hydroxy-1-methylethyl radical was generated in situ and added to (E)-1 with high anti-stereoselectivity. The bulkier is the γ-alkyl group of (E)-1, the higher does the selectivity become. Similarly, a radical addition to the acetates of (E)-1 and (E)-2 proceeded stereoselectively in an anti fashion, whereas (Z)-2 exhibited syn-stereoselectivity. The mechanism for these stereoselective radical additions is discussed.