Ethers, vinyl with organolithium reagents

Like magnesium, lithium reacts with alkyl halides, vinyl halides, and aryl halides to form organometallic compounds. Ether is not necessary for this reaction. Organolithium reagents are made and used in a wide variety of solvents, including alkanes. 

The cyclic vinyl ether 2,3-dihydro-1,4-dioxin is converted into its cyclic hemiacetal hydration product, tetrahydro-2-hydroxy-1,4-dioxin, in aqueous solution by an acid-catalyzed reaction <870K2746, 89JP043). Treatment of an alcohol with excess of 2,3-dihydro-1,4-dioxin at room temperature in the presence of copper(II) bromide in tetrahydrofuran leads to the corresponding acetal. This new protective group for alcohols, which is stable towards lithium aluminum hydride and organolithium reagents, can be removed by treatment with acidified aqueous methanol <85S806>. 

Organocuprates are generated from an organolithium reagent (see Chapter 15, Section 15.5) and a cuprous salt such as Cul (cuprous iodide). When two equivalents of n.-butyllithium are mixed with Cul in ether at -10°C, the product is lithium dibutylcuprate, 52. When 52 reacts with a conjugated ketone such as methyl vinyl ketone (10), the product is enolate anion 53, which gives 54... 

Metalation of the heteroaromatic compounds furan and thiophene with alkyllithi-um reagents furnishes the corresponding 2-lithio derivatives. For example, sequential treatment of 2-methylfuran with ABuLi in THF, followed by alkylation of the organolithium intermediate and hydrolysis of the resultant bis-vinyl ether, produces an unsaturated 1,4-diketone. 

Organolithium compounds and Grignard reagents are prepared by reaction of the metal with an alkyl, aryl, or vinylic halide, usually in diethyl ether or tetrahydrofuran as the solvent. 

---