Gilman cuprates reactions with ketones

So far only little is known about the mechanisms of such 1,4-additions. To start with, it is uncertain whether they only depend on the metal used or on both metal and substrate. At the beginning of the new millennium, however, the prototype of this reaction, i.e., the 1,4-addition of Gilman cuprates to a,fi-unsaturated ketones, could finally be assigned a mechanism after many years of studies and with a proper finish of crystallographic, NMR-spectroscopic, kinetic and quantum-chemical studies (Figure 10.46, see farther below). 

Fig. 10.46 (cont.) Mechanistic possibilities for the 1,4-addition of a Gilman cuprate to an a,/Lunsatitrated ketone. Part 2 shows the formation of the CuR-containing enolate (I) and its further reaction with typical electrophiles. The fact that all intermediates of this 1,4-addition are chiral, but generated in racemic form should not be overlooked consequently, the same is true of the final products J, K and L. 

Preferential 1,2-addition of Gilman s cuprate to a ketone over the usually much more facile 1,4-mode occurs in the case of keto enone (,67) When Goldsmith and Sakano treated (67) with 2 equiv. of Me2CuLi at —78 C and quenched the reaction with acetic anhydride, enone (66) was formed. At higher temperatures Michael addition begins to take place, although the cuprate also generates products of ketone enolization (68) rather than carbon-carbon bond formation (Scheme 10). 

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