Lithium bromide complexation with

Ethereal methyl1ithiurn (as the lithium bromide complex) was obtained by the submitters from Aldrich Chemical Company Inc. The checkers used 1.19 M methyl1ithiurn-lithium bromide complex in ether supplied by Alfa Products, Morton/Thiokol, Inc. The concentration of the methyllithium was determined by titration with 1.0 M tert-butyl alcohol in benzene using 1,10-phenanthroline as indicator. The submitters report that ethereal methyllithium of low halide content purchased from Alfa Products, Morton/Thiokol, Inc., gave similar results. 

Alternatively, a more nucleophilic anionic reagent can be generated by selective cleavage of a single trimethylsilyl group with methyl lithium-lithium bromide complex. This 1ithiobutadlyne derivative will react with electrophiles such as carbonyl compounds or primary alkyl iodides. 2... 

Selective desilylatiou of bis(trimethylsilyi)acetylenes. The methyllithium-lithium bromide complex reacts with 1 or 2 to afford the corresponding monolithium derivatives in nearly quantitative yield. These readily condense with aldehydes and ketones to afford alcohols in 46-90% yield. Note that different solvents are used for 1 and 2. Selective desilylation of 1 or 2 can also be effected with 1-10 mole % KF-18-crown-6 in the presence of a carbonyl compound. In this case, the yields of product are usually somewhat lower. ... 

Ring-opening reactions to yield aldehydes or ketones were reviewed [7-10]. Isomerization may be thermally induced [7] or may occur in the presence of basic or acidic agents [11]. Lithium bromide associated with tributylphosphine oxide or hexamethylphosphoric triamide (HMPA) has been used [12,13], but transition metal complexes may be more attractive [14-21]. In this work the performances of catalytic systems, e.g. "LiBr/HMPA/toluene", "Co2(CO) /MeOH", "NiBr2(PPh3)2/ Zn/PPh3/THF", etc. are compared for the isomerization of 3a and of analogues. Supported catalysts have also been studied. 

Synthesis of the perfluoroalkyl P-amino alcohol 5 (70) required for the preparation of the perfluoroalkyl ketone VI as shown in Scheme 2 is illustrative of the method used to prepare analogous compounds. Tm-butyloxycarbonyl-L-cyclohexylalaninal 4 was condensed with perfluoroethyl or perfluoropropyl lithium which was generated in situ by the addition of methyllithium-lithium bromide complex to the corresponding perfluoroalkyl iodide. The alcohol 5 was isolated as an epimeric mixture which was used in the preparation of peptide IV. Oxidation using the Dess-Martin periodinane reagent (9) yielded the fluoroketone VI. 

In 1947 Wittig and Wetterling 162> examined the reaction between tetra-methylammonium bromide and phenyllithium in ether in an effort to prepare tetramethylammonium phenyl. None of the desired product was obtained, but benzene was formed along with an insoluble material which was characterized as the lithium bromide complex of the ylid on the basis of its reactions with water, iodine, methyl iodide, and benzophenone. 

The same material is also obtained when bromomethyltrimethyl-ammonium bromide is treated with phenyllithium in ether. Although the lithium bromide complex of the ylid is insoluble in ether, the solid can be dissolved in tetrahydrofuran (THF) in concentrations up to 0.9 M 39>. 

Daniel and Paetsch carried out a reaction of the lithium bromide complex of trimethylammoniummethylide with diphenylmercury to clarify the structure of the ylid in solution. Previously Gilman and Jones 49> as well... 

Earlier, we reported that complexes of lithium bromide (LiBr) with copolyether-urethane-ureas led to the formation of hydrogels (6). The water absorption curves for these hydrogels indicated the existence of two modes of absorption an initial water absorption that depended on the concentration ratio of LiBr to the urethane-urea segment (hard segment) of the block copolymer, and the water uptake at higher salt concentration which was attributed to the formation of voids in the film. 

In the remainder of this chapter, particular reactions are selected for examination of their synthetic potential. Acetylide ions are useful for linking carhon chains, particularly where a double bond is desired with stereoselectivity. Acetylene and 1-alkynes may be deprotonated with strong bases such as LDA and then treated with alkyl halides or carbonyl compounds. Preformed lithium acetylide complexed with ethylenediamine is available as a dry powder. Several alkynes derived from acetylide and carbon dioxide or formaldehyde are available, including propargyl alcohol (HC CCHjOH), propargyl bromide (HC CCH Br), and methyl propio-late (HC=CC02CH3). 

Stevens rearrangements proceed smoothly whenever a benzylic group is migrating. For example, ethereal phenyllithium readily deprotonates tetramethylammon-ium bromide to give the lithium bromide-complexed ylide. This species reacts with a variety of electrophiles such as benzophenone, methyl iodide, or molecular iodine. But when the suspension is shaken in a sealed tube for 90 h at ambient temperature, the ylide decomposes entirely to trimethylamine and polymethylene (up to 74%) irrespective of the solvent used (DEE, THE, glyme). The same kind of degradation occurs when phenyllithium is replaced by -butyllithium or phenylsodium. ... 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

Although ethereal solutions of methyl lithium may be prepared by the reaction of lithium wire with either methyl iodide or methyl bromide in ether solution, the molar equivalent of lithium iodide or lithium bromide formed in these reactions remains in solution and forms, in part, a complex with the methyllithium. Certain of the ethereal solutions of methyl 1ithium currently marketed by several suppliers including Alfa Products, Morton/Thiokol, Inc., Aldrich Chemical Company, and Lithium Corporation of America, Inc., have been prepared from methyl bromide and contain a full molar equivalent of lithium bromide. In several applications such as the use of methyllithium to prepare lithium dimethyl cuprate or the use of methyllithium in 1,2-dimethyoxyethane to prepare lithium enolates from enol acetates or triraethyl silyl enol ethers, the presence of this lithium salt interferes with the titration and use of methyllithium. There is also evidence which indicates that the stereochemistry observed during addition of methyllithium to carbonyl compounds may be influenced significantly by the presence of a lithium salt in the reaction solution. For these reasons it is often desirable to have ethereal solutions... 

Some instances of incomplete debromination of 5,6-dibromo compounds may be due to the presence of 5j5,6a-isomer of wrong stereochemistry for anti-coplanar elimination. The higher temperature afforded by replacing acetone with refluxing cyclohexanone has proved advantageous in some cases. There is evidence that both the zinc and lithium aluminum hydride reductions of vicinal dihalides also proceed faster with diaxial isomers (ref. 266, cf. ref. 215, p. 136, ref. 265). The chromous reduction of vicinal dihalides appears to involve free radical intermediates produced by one electron transfer, and is not stereospecific but favors tra 5-elimination in the case of vic-di-bromides. Chromous ion complexed with ethylene diamine is more reactive than the uncomplexed ion in reduction of -substituted halides and epoxides to olefins. ... 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

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