title: Regio- and stereoselectivity in the reactions of organometallic reagents with an electron-deficient and an electron-rich vinyloxirane: applications for sequential bis-allylic substitution reactions in the generation of vicinal stereogenic centers.
abstract: Vinyloxiranes provide opportunities for bis-allylic substitution reactions and the generation of new vicinal stereogenic centers if regio- and stereocontrol can be achieved. Ethyl (E)-4,5-epoxy-2-hexenoate affords excellent S(N)2':S(N)2 regioselectivity and anti:syn product diastereoselectivity with dialkyzinc reagents in the presence of CuCN, and conversion of the resultant allylic alcohol to the acetate affords good syn:anti product diastereoselectivity in S(N)2'-selective allylic substitutions with alkylcyanocuprates in THF. (E)-1-(tert-Butyldimethylsilyloxy)-2,3-epoxy-4-hexenonate gives excellent S(N)2':S(N)2 regioselectivity and anti:syn product diastereoselectivity with dialkyzinc reagents in THF or DMF or Grignard reagents in Et(2)O/THF (10/1) in the presence of CuCN. Conversion of the product allylic alcohol into the allylic phosphate affords excellent S(N)2' regioselectivity and syn:anti product diastereoselectivity with lithium alkylcyanocuprates for primary and secondary alkyl transferable ligands, while S(N)2 regioselectivity is observed for the tert-butyl ligand. Reaction conditions have been developed for regio- and stereocontrolled bis-allylic substitution reactions on both electron-rich and electron-deficient alkenyloxiranes, providing a methodology for the generation of vicinal alkane stereogenic centers.
authors.affiliation: Hunter Laboratory, Department of Chemistry, Clemson University, Clemson, South Carolina 29634-0973, United States. dieterr@clemson.edu
authors.forename: R Karl
authors.initials: RK
authors.lastname: Dieter
authors.forename: Yaxin
authors.initials: Y
authors.lastname: Huang
authors.forename: Fenghai
authors.initials: F
authors.lastname: Guo