Lithium dialkylcopper reagents

Lithium dialkylcopper reagents couple with allylic acetates to give normal coupling products or those resulting from allylic rearrangement, depending on the... 

Lithium dialkylcopper reagents can be prepared by mixing 2 mol of RLi with 1 mol of a cuprous halide in ether at low temperamres ... 

Lithium dialkylcopper reagents can be oxidized to symmetrical dimers by O2 at -78°C in THF. The reaction is successful for R = primary and secondary alkyl, vinylic, or aryl. Other oxidizing agents (e.g., nitrobenzene) can be used instead of O2. Vinylic copper reagents dimerize on treatment with oxygen, or simply on standing at 0°C for several days or at 25°C for several hours, to yield LS-dienes." ... 

Neither Grignard reagents nor lithium dialkylcopper reagents generally add to ordinary C=C double bonds. An exception is the reaction of (PhMe2Si)2 Cu(CN)Li to 8-oxabicyclo[3.2.1]oct-2-ene derivatives. Grignard reagents usually add only to double bonds susceptible to nucleophilic attack (e.g., fluoroalkenes and... 

Addition of lithium dialkylcopper reagents to dithiocarboxylic esters... 

Among other methods for the preparation of alkylated ketones are (1) the Stork enamine reaction (2-19), (2) the acetoacetic ester synthesis (0-94), (3) alkylation of (3-keto sulfones or sulfoxides (0-94), (4) acylation of CH3SOCH2 followed by reductive cleavage (0-109), (5) treatment of o-halo ketones with lithium dialkylcopper reagents (0-87), and (6) treatment of a-halo ketones with trialkylboranes (0-99). 

Whether 1,2 or 1,4-addition occurs depends upon a number of factors, such as the precise reagent used, and any steric factors present on the substrate. Thus, for example, lithium dialkylcopper reagents usually undergo 1,4-addition. However, Grignard reagents usually add in a 1,2-manner to aldehydes but with conjugated ketones, steric factors are important, as illustrated below. 

If an alkyl copper is treated with an alkylUthium, a lithium dialkylcopper reagent can be formed. Alternatively, treatment of a copper halide (e.g., cuprous iodide, Cul) with an alkylhthium (e.g., n-butylhthium, CH3CH2CH2CH2L1) produces the same reagent (Equation 7.25). 

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