Highly Diastereoselective Radical Cyclizations on Soluble Ring Opening Metathesis Supports

This study represents the first examples of stereoselective radical cyclizations on soluble supports. A stereocontrol element consisting of a polymer-imbedded (+)-isosorbide chiral auxiliary was used in each monomer subunit. A survey of various Lewis acids was also examined. The best results gave very high distereoselectivites of >100:1 in a hepa-1,3-dienenyl radical cyclization using zinc chloride as a Lewis acid

Highly Diastereoselective 5-Hexenyl Radical Cyclizations with Lewis Acids and Carbohydrate Scaffolds

Carbohydrates as removable chiral scaffolds for free radical cyclizations were examined for the first time. This investigation illustrates the utility of two inexpensive carbohydrate derivatives as sources of asymmetry for 5-hexenyl radical cyclizations. Diastereomeric ratios as high as 100:1 were achieved with an ester-appended (+)-isosorbide hexose and 70:1 for a diol-protected d-xylose pentose. Temperature dependence, Lewis acids, and solvents were all examined. By correlation with known compounds, the newly generated chiral centers were of the (S)-configuration