Substitutions halides, lithium cuprate

The conjugate addition reactions probably occur by a mechanism similar to that for substitution on allylic halides. There is probably an initial complex between the cuprate and enone.44 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.45 Solvent... 

Secondary and tertiary dialkylcuprates, lithium dialkenyl-, and even diphenyl-cuprates, add in very good yields to the reactive propionaldehyde diethyl acetal. The syn addition products may be trapped with a variety of electrophiles such as alkyl, alkenyl, alkynyl and aryl halides. The method has been used for the synthesis of several natural products. Substituted alkynic acetals also react with lithium dialkylcuprates in ether to furnish stable dialkenylcuprates of type (128) which do not eliminate to the corresponding alkoxy allenes (129) if the temperature is maintained below -20 C.164-179... 

Nucleophilic Substitutions of Halides. Although unreactive with benzyl bromide and vinyl iodides, lithium (3,3-diethoxy-l-propen-2-yl)(phenylthlo)cuprate undergoes clean substitutions with allyllc bromides to afford 1,4-dienes (eq 1). The mixed homocuprate lithium (3,3-diethoxy-l-propen-2-yl)(3,3-dlmethyl-l-bulynyl)cuprate provides similar results. ... 

Substitution reaction of alkyl halide with lithium dialkyl cuprates (9.8)... 

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