Oxygenated organolithiums

VI. OXYGENATED ORGANOLITHIUMS INTRAMOLECULAR COMPLEXATION AND ENTHALPIES OF FORMATION... 

As pointed out in Note 1 a nitrogen atmosphere is preferred for the preparation of organolithium compounds. In the present example exclusion of oxygen is attained fairly satisfactorily by keeping the solution at the reflux point throughout an atmosphere of ether vapour is thus maintained. 

In ether or tetrahydrofuran organolithium reagents cleave the silicon-oxygen bond in hexamethylphosphoramide, they react at the carbon atom. ... 

By application of the most common procedure—i.e by using an a-silylated organolithium or magnesium reagent—the /3-hydroxysilane 5a/5b can be isolated. However in the case of M = Na or K, the alkoxide oxygen in 4a/4b is of strong ionic character, and a spontaneous elimination step follows to yield directly the alkene 3. 

The addition reactions of alkyllithium-lithium bromide complexes to a-trimethylsilyl vinyl sulfones that have as a chiral auxiliary a y-mono-thioacetal moiety derived from ( + )-camphor are highly diastereoselective. A transition state that involves chelation of the organolithium reagent to the oxygen of the thioacetal moiety has been invoked. The adducts are readily converted via hydrolysis, to chiral a-substituted aldehydes22. 

J-Oxygen-functionalised sp3 organolithium compounds react with alkenyl-carbene complexes to generate the corresponding cyclic carbene complexes in a formal [3+3] process (see Sect. 2.8.1). In those cases where the organolithium derivative contains a double bond in an appropriate position, tricyclic ether derivatives are the only products isolated. These compounds derive from an intramolecular cyclopropanation of the corresponding cyclic carbene complex intermediate [89] (Scheme 83). 

Heterocyclic systems, such as the substituted indoline illustrated below,13 may also be constructed via cyclization of unsaturated organolithiums and a recent review of the preparation of nitrogen- and oxygen-containing heterocycles via this approach is available.14... 

Addition of an organolithium and Grignard reagent across the peroxy bridge of endoperoxides gives c/s-cyclohex-2-en-l,4-diols. Alkyl, cycloalkyl, alkenyl and aryl moieties can be transferred to oxygen <96TL6635>. 

Organolithium compounds can add to a, (3-unsaturated ketones by either 1,2- or 1,4-addition. The most synthetically important version of the 1,4-addition involves organocopper intermediates, and is discussed in Chap 8. However, 1,4-addition is observed under some conditions even in the absence of copper catalysts. Highly reactive organolithium reagents usually react by 1,2-addition, but the addition of small amounts of HMPA has been found to favor 1,4-addition. This is attributed to solvation of the lithium ion, which attenuates its Lewis acid character toward the carbonyl oxygen.111... 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

Similar methods also generate the selenium and oxygen analogues 3370) and 34 71), respectively, as outlined in Eq. 37 and 38. These organolithium species add to carbonyl groups of non-conjugated and conjugated aldehydes and ketones, frequently... 

Hodgson DM, Stent MAH (2003) Overview of Organolithium-Ligand Combinations and Lithium Amides for Enantioselective Processes. 5 1-20 Hodgson DM, Tomooka K, Gras E (2003) Enantioselective Synthesis by Lithiation Adjacent to Oxygen and Subsequent Rearrangement. 5 217-250... 

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