s-412 % Gotebofg, swedell
Organ~pper xeagenU of diffenmt compositions are highly useful tools in organic synthesis for the formation of new carbon -carbon bonds.1 Cons&able effort has been spent in attempts to achieve high stereoselectivityinthebolKlformation.
Enan~vityviachiralauxilipritsindlecopperreagentpor ligands is an elusive field with some striking examples of success.2 Diasmvity via chirality in the organic substrate has proved to be a more accessible route1
Oureffortshave~ndirectsdtowardsabetterunderstandingof~mechanianforthecarbon-carbon bond formation between the organocopper nzagent, mostly R$Ui. and enones or enoate&
We have shown by NMR qeumscopy that the reversible formation of a n-complex between copper in the organocvpper reagent and the alhe 1c-orbMs of the enoate probably is an early step in the reaction leading to the carbon -carbon bond.3 It has later been shown that alkene-copper xcomplex formation also takes place on addition of Me$uL.i to enon& and enynoates.5 llms z-complex formation is probably a general reaction thathtiStObethIlilltO2lCCOllUthdiSCUSSiOilSCO-g the tmdmism of carbon-carbon bond formation to aikenes activated by electmn withdmwing groups.
Furthermore we have observed that the reactivity of the cqper magents and the chemoselectivity of dre reactions anz strongly tiuenced by the choice of solvent6 Also. in a noncoordjnatiag solvent as Muene or dichloromethane the presence of a chiral amino group can exert a strong intluence on the diastcreoselectivity 13173