title: Regio- and stereocontrol in the reactions of α-halo-β,γ-enoates and α-O-phosphono-β,γ-enenitriles with organocuprates.
abstract: The reactions of (Z)- and (E)-ethyl 2-chloro-3-octenoate (4a and 17) and (E)- and (Z)-diethyl (1-cyano-2-heptenyl)phosphate (21a and 21b) with organocuprates were investigated as potential substrates for preparing γ-substituted α,β-enoates and enenitriles. In these copper-mediated allylic substitution reactions, the Z-isomer 4a displayed complete regio- and stereoselectivity (i.e., E:Z), while the regio- and stereoselectivity for E-isomer 17 varied as a function of solvent, cuprate reagent, transferable ligand, and cuprate counterion (e.g., Li(+) vs MgX(+)). Excellent selectivities could be achieved with 17 and (n)BuCuCNLi in Et2O. Conditions for improved selectivities in the reactions of allylic cyanophosphates over those previously reported were found. A series of relative rate and competition experiments was performed, and the degree of regio- and stereoselectivity for each system was rationalized in the light of the current mechanistic understanding of cuprate-mediated allylic substitution reactions.
authors.affiliation: Hunter Laboratory, Department of Chemistry, Clemson University , Clemson, South Carolina 29634-0973, United States.
authors.forename: R Karl
authors.initials: RK
authors.lastname: Dieter
authors.forename: Alfredo
authors.initials: A
authors.lastname: Picado