Esters reaction with organocopper reagents

Addition to ot, -acetylenic esters and ketones (3, 108 6, 163-164). The addition of organocopper reagents to conjugated acetylenic carbonyl compounds is usually not stereospeciflc, although cis-addition predominates. Japanese chemists have found that the stereoselectivity in the reaction with alkylcopper reagents is markedly enhanced by use of the complex RCu BRj. Thus the reaction of dimethyl acetylenedicarboxylate with n-butylcopper complexed with tri-n-butylboron (or triethylboron) results in exclusive formation of the cis-adduct. In the absence of a trialkylborane the cis- and adducts are formed in the-ratio 85 15. 

Homoconjngate addition to cyclopropanes. Corey and Fuchs have investigated the reaction of cyclopropanes with organocopper reagents as a possible synthetic route to prostanoids. For example, the tricyclic lactone ester (1) reacts with divinylcopper-lithiura (2.0 eq.) in ether at -12° (19 hr.) to give the vinylcyclopentane lactone ester (2). Tliis product was treated directly with lithium iodide (5 eq.) in pyridine (1,615-616) at reflux for 3 hr. to give the lactone (3) in about 37% yield. 

Some of the Lewis acid catalyzed Michael additions to a,3-unsaturated carbonyls can also be rationalized based on these models. For example, BFs-mediated additions of organocopper reagents to chiral a,3-unsaturated esters such as (-)-8-phenylmenthyl crotonate (35) occur with high levels of dia-stereoselectivity. " The product stereochemistries for these reactions could be predicted by assuming the reactive conformation (35S), which follows the basic structural tenets of model A (Figure 41). ... 

---