Gilman reagent reaction with alkyl halides

Explain why tertiary alkyl halides cannot be used in coupling reactions with Gilman reagents. 

Alkanes can also be prepared from alkyl halides by reduction, directly with Zn and acetic acid (AcOH) (see Section 5.7.14) or via the Grignard reagent formation followed by hydrolytic work-up (see Section 5.7.15). The coupling reaction of alkyl halides with Gilman reagent (R 2CuLi, lithium organocuprates) also produces alkanes (see Section 5.5.2). 

Alkanes, RH (Sec. 7.7) (Sec. 10.7) (Sec. 10.8) (Sec. 19.9) from alkenes by catalytic hydrogenation from alkyl halides by protonolysis of Grignard reagents from alkyl halides by coupling with Gilman reagents from ketones and aldehydes by Wolff-Kishner reaction... 

Alkylbenzenes with straight-chain alkyl groups can also be prepared by means of the coupling reactions you saw in Section 12.12. One of the alkyl groups of a Gilman reagent can replace the halogen of an aryl halide. 

Lithium dialkylcuprate reagents (Gilman reagents) are formed by the reaction of two equivalents of an organolithium reagent with cuprous iodide. Reaction of the dialkylcuprate with an alkyl, aryl, or vinyl halide forms a new carbon-carbon bond. 

Reaction of a Gilman reagent with an alkyl halide (Section 12.12). 

Another transition metal-catalyzed carbon-carbon bond-forming reaction we shall discuss is the Corey—Posner, Whitesides-House reaction. Using this reaction an alkyl halide can be coupled with the alkyl group from a lithium dialkyl cuprate reagent (often called a Gilman reagent). This reaction does not have a catalytic mechanism. 

The Corey—Posner, Whitesides—House reaction involves the coupling of a hthium dialkyl-cuprate (called a Gilman reagent) with an alkyl, alkenyl, or aryl halide. The alkyl group of the lithium dialkylcuprate reagent may be primary, secondary, or tertiary. However, the halide with which the Gilman reagent couples must be a primary or cychc secondary alkyl halide if it is not alkenyl or aryl. 

Gilman reagents are prepared by the reaction of a copper(l) halide with two equivalents of an alkyl- or aryllithium in diethyl ether or tetrahydrofuran. 

Some reactions of the Gilman reagent with an alkyl halide occur in two steps, not by an Sj 2 mechanism. A two-step sequence occurs when a dialkyl cuprate reacts with an alkyl iodide. 

---