1,2- and 1,5-Stereocontrols in 5-Hexenyl Radical Cyclizations: Cooperative or Antagonist Effect. Conformation Experimental Results with MM2 Calculations of Transition States

Article abstract of DOI:10.1021/jo00124a012

The cyclofunctionalization of 1,6-dienes 1 and 2 via the addition of tosyl radical allows the analysis of the combined effects of 1,2- and 1,5-stereocontrols on the outcome of 5-hexenyl radical cyclizations.MM2 calculations of the transition states agree quite well with the experimental selectivity, i.e., exclusive 1,2-trans control, and predominance of 1,5-cis over 1,5-trans relationship.The addition of TsBr to carbohydrate-derived epimeric dienes 3a and 3b shows that the stereochemistry of the newly formed C-C bond is controlled by the configuration of the C2 center of the radical. 1,5-trans or 1,5-cis selectivity can be achieved depending on the configuration of C2.