Cyanocuprate reagents

Indol-2-ylcopper reagents can also be prepared from 2-lithioindoles and they have some potential for the preparation of 2-substituted indoles. 1-Methyl-indol-2-ylcopper can be prepared by reaction of 2-lithio-l-methylindole with CuBr[10]. It reacts with aryl iodides to give 2-aryl-1-methylindoles. Mixed cyanocuprate reagents can be prepared using CuCN[ll], The cyan-ocuprate from 1-methylindole reacts with allyl bromide to give 2-allyl-l-methylindole. 

Scheme 6.40. Influence of alkene geometry on stereoselectivity of allylic substitution of mesylates 189 and 192 with boron trifluoride-modified lower order cyanocuprate reagents.

These reagents are qualitatively similar to other cuprates in reactivity, but they are more stable than the dialkylcuprates. Because cyanocuprate reagents usually transfer only one of the two organic groups, it is useful to incorporate a group which normally does not transfer. The 2-thienyl group has been used for this purpose.9 In a mixed alkyl-thienyl cyanocuprate, only the alkyl substituent is normally transferred as a nucleophile. 

Dichloropropenoyl trimethylsilane, prepared by photochemically induced addition of bromotrichloromethane to the ethyl enol ether of acetyl trimethylsilane, undergoes completely regioselective addition-elimination upon treatment with lithium cyanocuprate reagents, giving the Z -3-chloroalk-2-enoyl silane products (vide supra, Section III.D.3)135. 

Table 1. Reaction of Cyanocuprate Reagents with Epoxy Vinyl Sulfoxides...

CuCN, and BF3 0(02115)2. The BF3 appears to interact with the cyanocuprate reagent, giving a more reactive species. The efficiency of the reaction is improved by the addition of trialkylphosphines to the reaction mixture." Even reagents prepared from a 1 1 ratio of organocopper and organolithium compounds are reactive in the presence of phosphines." ... 

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