Alkane Synthesis Using Organocopper Reagents

Two of the groups bonded to the hydroxyl-bearing carbon of the alcohol are the same because they are derived from the Grignard reagent. For example, 

PROBLEM 14.8 What combination of ester and Grignard reagent couid you use to prepare each of the foiiowing tertiary aicohois  

SAMPLE SOLUTION (a) To appiy the principies of retrosynthetic anaiysis to this case, we disconnect both ethyi groups from the tertiary carbon and identify them as arising from the Grignard reagent. The phenyi group originates in an ester of the type C6H5CO2R (a benzoate ester). 

OrganometalUc compounds of copper have been known for a long time, but their versatility as reagents in synthetic organic chemistry has only recently been recognized. The most useful organocopper reagents are the lithium dialkylcuprates, which result when a copper(l) halide, reacts with two equivalents of an alkyllithium in diethyl ether or tetrahy-drofuran. 

Copp0r(l) salts are also known as cuprous salts. 

In the first stage of the preparation, one molar eqnivalent of alkyllithium displaces halide from copper to give an alkylcopper(I) species  

Lithium dialkylcuprates react with alkyl halides to produce alkanes by carbon-carbon bond formation between the alkyl group of the alkyl halide and the alkyl group of the dialkylcuprate  

Methyl and primary alkyl halides, especially iodides, work best. Elimination becomes a problem with secondary and tertiary alkyl halides  

Step 1 One molar equivalent of an alkyllithium reagent displaces iodide from 

Step 2 The second molar equivalent of the alkyllithium adds to the alkylcopper to give a negatively charged R2Cu species called a dialkylcuprate. It is formed as its lithium salt, a lithium dialkylcuprate. 

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