Lithium diorganocuprates

The stereoselective 1,4-addition of lithium diorganocuprates (R2CuLi) to unsaturated carbonyl acceptors is a valuable synthetic tool for creating a new C—C bond.181 As early as in 1972, House and Umen noted that the reactivity of diorganocuprates directly correlates with the reduction potentials of a series of a,/ -unsaturated carbonyl compounds.182 Moreover, the ESR detection of 9-fluorenone anion radical in the reaction with Me2CuLi, coupled with the observation of pinacols as byproducts in equation (40) provides the experimental evidence for an electron-transfer mechanism of the reaction between carbonyl acceptors and organocuprates.183... 

Diastereoselectivities observed for 1,2-additions of carbon nucleophiles, and 1,4-additions of lithium diorganocuprates, to enantiomerically enriched bicyclo[m.l.O]alk-3-en-2-ones possessing 8-, 12-, and 15-membered rings have been discussed. ... 

In an effort to demonstrate the synthetic utility of vinyliodonium salts, small-scale reactions of (4-rm-butyl-1 -cyclohexenyl)phenyliodonium tetrafluoroborate (62) with various nucleophilic species, especially copper(I) reagents, have been conducted125,126. The copper(I)-assisted reactions include the conversions of 62 to 1-cyano-, 1-halo-, 1-alkyl- and 1-phenyl-4-ter r-butylcyclohexenes (equation 215). The alkylation and phenylation of the cyclohexenyl ligand in 62 with lithium diorganocuprates is noteworthy, since the treatment of 62 with H-butyllithium leads to fragmentation of the iodonium ion and affords only a 0.2% yield of 1 -w-butyl-4-terr-butylcyclohexene (equation 216)126. 

If conjugate addition of an organometallic nucleophile is desired, this can be accomplished by using a lithium diorganocuprate reagent, which has the organic group at-... 

The reactions of lithium diorganocuprates with a./3-unsaturated carbonyl compounds give excellent yields of 1.4-addition products ... 

If the compound is a,/3-unsaturated, remember to consider the jS-carbon as the electrophile, resulting in 1,4-addition (conjugate addition). Amines, HCN, and lithium diorganocuprate nucleophiles result in 1,4-addition products. 

The coupling of j8-bromostyrene with lithium diorganocuprates at a low temperature was also accompanied by reduction and elimination as important side reactions (309). The reaction is summarized by Eq. (54). 

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