Organolithium compounds with oxygen

The reaction of organolithium compounds with oxygen can be controlled to give, at low temperatures, a hydroperoxide or at higher temperatures an alcohol or phenol [43]. 

There are several examples of a-oxygen- and nitrogen-functionalized organolithium compounds with sp and sp hybridization in acyclic and cyclic systems of general structures I-IV. These compounds show a tendency to undergo a-elim-ination processes to generate carbene intermediates. 

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). 

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. 

Exposure of alkyllithium or aryllithium compounds to the atmosphere may cause degradation due to reaction with oxygen (equation 1) or air moisture (equation 2). Certain organolithium compounds are unstable at room temperature in the neat form, and require dilution even then they should best be stored at low temperature. The instability may be the result of reactions such as the eliminations depicted in equations 3 and 4, taking place as the temperature rises . 

Configurational stability has also been confirmed for various metalated carbamates by Hoppe and coworkers. Remarkably, carbamate-protected alcohols such as 20 are deprotonated enantioselectively, when treated with i-butyllithium in the presence of (—)-sparteine. The lithium carbenoids like 21 (R = alkyl) thus generated turn out to retain their configuration (equation 11). Similar results have been obtained for a-lithiated amines and carbamate protected amines " . As a rule, dipole stabilization of the organolithium compounds in general also enhances the configurational stability of a-oxygen-substituted lithium carbenoids. 

The synthesis of oxygen- and nitrogen-containing heterocyclic compounds by anionic cyclization of unsaturated organolithium compounds has been reviewed recently. " Broka and Shen reported the first intramolecular reaction of an unstabilized a-amino-organolithium compound using reductive lithiation of an A,5-acetal derived from a homoaUylic secondary amine (Scheme 21). Just one example was reported treatment with lithium naphthalenide gave the pyrrolidine product, predominantly as the cis isomer. 

A great nnmber of chiral bidentate nitrogen and oxygen ligands, which served well with other cations than lithinm, are known . Only very limited success was achieved with organolithium compounds in the classical examples of addition reactions onto aldehydes 335-337... 

Organolithium compounds can yield more than one product with R3Si Co(CO)4 equimolar amounts give an adduct resulting from nucleophilic attack by R8- on oxygen of a fraras-carbonyl group (entry 23 compare Sections III,B,7 and III,F,1). 

Many organolithium compounds are useful reagents and no doubt many more would be if only they could be made. Tin chemistry allows us to make organolithium compounds that cannot be made by direct lithiation. An excellent example is a lithium derivative with an oxygen atom on the same carbon. The hydrogen atom is not particularly acidic and cannot be removed by BuLi, while the bromide is unstable and will not survive treatment with BuLi. 

Reductive 1,2-eIimination of chlorine and bromine from adducts of l-bromo-2-chlorocyclo-propene (see Section 5.2.2.1.2.5.) with oxygen and sulfur hetarenes has served in the synthesis of a number of cycloproparenes. This transformation is effected by low-valent titanium together with lithium aluminum hydride or an organolithium compound. Thus, reaction of the adduct 3 of l-bromo-2-chlorocyclopropene and 1,3-diphenylisobenzofuran with tita-nium(III) chloride and lithium aluminum hydride overnight in tetrahydrofuran led to elimination of both halogens together with extrusion of the oxygen and formation of 2,7-diphenyl-l/f-cyclopropa[ ]naphthalene (4) in 72% yield. 

Cyclic alkyl aryl ethers lead also to functionalized organolithium compounds by reductive carbon-oxygen bond cleavage in arene-catalyzed lithiation process. Thus, the treatment of 2,3-dihydrobenzofuran (47) with an excess of lithium in the presence of a catalytic amount of DTBB in THF at 0°C gives the dianion (48) which after reaction with different carbonyl compounds and final hydrolysis with water leads to... 

---