Lithium dimethylcuprate structure

The reaction of lithium dimethylcuprate with 17-A shows considerable 1,4-diastereoselectivity. Offer an explanation, including a transition structure. 

In an approach to the stereocontrolled creation of the acyclic side-chain of tetracyclic triterpenoids and other natural products, Trost and his colleagues have converted the acyclic starting compound (29) into the cyclopropanoid intermediate (31) via the diazo-ketone (30). The key step in the scheme is the cleavage of the cyclopropane with lithium dimethylcuprate to give (32). The stereochemistry at C-7 is determined by the configuration of the double bond in (29). The c.d. and u.v. spectra of a series of triterpenoid olefins have been measured. The Scott-Wrixon rules can be used to correlate the sign of the c.d. curves with molecular structure. A... 

A related structure 15 with the lactone ring across one side of the cyclopropane was converted to a spirocyclic system 16 upon treatment with lithium dimethylcuprate. ... 

The difficulties of direct oxidative insertion with metals other than Mg or Li mean that o-complexes are often made from organo-lithium or Grignard reagents by metal exchange. This reaction amounts to a nucleophilic substitution at the metal without a change of oxidation state so the metal is used in whatever oxidation state is finally needed. Attack of methyl lithium on a Cu(I) halide gives methyl copper 50, a o-complex of Me- and Cu(I). If an excess of MeLi is present an ate complex is formed, lithium dimethylcuprate 51. This is formally a compound of a copper anion 51a, just as BF4 is a borate. The term ate complex refers to such formally anionic complex in which the metal has one extra anionic ligand. Its true structure is dimeric 51b and it exists as an equilibrium with 52 in solution.20... 

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 ... 

Draw the structure of the product of a reaction between lithium dimethylcuprate and ethyl acrylate. 

The species from the 2 1 mole ratio are known as cuprates and have been the most useful synthetic reagents. In solution lithium dimethylcuprate exists as a dinier [LiCulCHslalz, but the precise structure of the reagent is not known. It is often represented as four methyl groups attached to a tetrahedron of metal atoms. 

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