Lithium dimethylcuprate stability

Few comparisons have been made among the relative stabilities of other classes of organocopper compounds. Generally, for simple derivatives, the order of decreasing stability is RC=CCu > Aryl-Cu > Alkyl-Cu. For vinylcopper compounds, 2-butenylcopper is more stable than propenylcopper 294). The higher homologs of methylcopper and lithium dimethylcuprate are less stable (69, 276, 297). 

The substrate given in question 19 is subjected to reaction with lithium dimethylcuprate. Please write the structures of all the possible products and calculate their relative energies by taking 0.9 kcal/mol for 1,3-diaxial interaction between a methyl and a hydrogen. Which product will you predict to predominate if allowed to consider the product s thermodynamic stability as the primary control factor ... 

In a study of electron-transfer reactions. House has examined the stabilities of the anion radicals derived from a number of y-cyclopropyl-ap-unsaturated ketones. It would appear that for the conversion of substrates containing the unit depicted by (240) into (241) a rearrangement rate in excess of 10 s is necessary in order to detect the anion radical intermediate present in metal-ammonia reductions. A rate of ca. 10 s is likewise required in lithium dimethylcuprate reactions. ... 

A study of 1,2-versus 1,4-addition to a series of cyclopenten-l-ones bearing a-donor substituents (X = H, Cl, Br, OMe, pyrrolidin-l-yl, SPh, and SePh) at position 2 has established that MeLi gives 1,2-adducts in 28-75% yield and no 1,4-adduct, lithium dimethylcuprate gives only 1,4-addition (51-76%), and cyanomethyl lithium gives mainly 1,2-adducts (43-60%). Theoretical calculations reveal that the predominance of 1,2-attack in the reactions involving MeLi and cyanomethyllithium cannot be explained by the relative thermodynamic stabilities of the products. 

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