Bromide lithium, complex with

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. ... 

US patent 6,677,453, Production of polymorphic forms I and II of finasteride by complexation with group I or II metal salts [97]. Finasteride Form I of was prepared by first forming a substantially insoluble complex of the compound and a Group I or Group II metal salt (such as lithium bromide), and then dissociating the complex by dissolving away the salt component with water to obtain substantially pure crystalline finasteride Form I. 

Reviews covering the chemistry of group 2 metal complexes with phosphorus-stabilized carbanions,279 and of molecular clusters of magnesium dimetallated primary phosphanes, are available.2 u Magnesium phosphanes remain rare compounds.281 Lithiation of bromide 98 with BuLi in the presence of tmeda in pentane produces a lithium phosphine dimer subsequent treatment with MgCl2 in EtzO gives the phosphane 99 in 69% overall yield (Equation (19)). The centrosymmetric 99 has Mg-C = 2.217 A Mg-P = 2.77 A (av.).282... 

CH3(CH2)4CH = CHCH = CHC00CH2CH3, C12H20O2, Mr 196.29, bp6i> 70-72 °C, has been identified in pears and has the typical aroma of Williams pears. Synthesis of ethyl 2-trans-4-cw-decadienoate starts from cis-l-heptenyl bromide, which is converted into a 1-heptenyllithium cuprate complex with lithium and copper iodide. Reaction with ethyl propiolate yields a mixture of 95% ethyl 2-trans-A-cis- and 5% ethyl 2-tranx-4-tranx-decadienoate. Pure ethyl 2-trans-A-cis-decadienoate is obtained by fractional distillation [25]. A biotechnological process for its preparation has been developed [26]. 

Methyllithium complexed with lithium bromide (1.5-molar Et20) is preferred over uncomplexed methyllithium owing to its greater stability (Aldrich). 

There is no doubt that in these. reactions the nitrogen atom of the pyridine ring is complexed with either the lithium alkyl or aryl or with the lithium bromide which is usually present in many preparations of organolithium compounds. It has been established that, either in the presence of an excess of lithium bromide or in the total absence of this salt, phenyllithium still gives the same ortho .para ratio on reaction with 3-picoline.229 To account for the predominant formation of the 2,3-isomer in the reaction of CH3Li with 3-alkylpyridines, it was suggested261 that the transition states for these reactions were similar... 

To achieve this goal, (—)-carvone was transformed into the dimethylhydrazone, and the unsaturated hydrazone was deprotonated by EDA (Scheme 37). Due to complexation of the lithium ion with nitrogen, 3,3-dimethoxypropyl bromide was used to alkylate the a-position (202). A 3 2 mixture of the two possible stereoisomers 332 and 333 was obtained. The authors claimed that the ketone was... 

Reactions of the corresponding ketones have been much less studied, but alkylation reactions appear to be highly antiselective relative to the metal. Some alkylations resulting in the isomerization of the diene geometry have been observed. For example, reaction of (85) with methyl magnesium bromide gives (86) but reaction with methyl lithium affords (87) (Scheme 137). Related reductions of dienone iron complexes with sodium borohydride are also highly antiselective. 

This methodology has also been applied to the alkylation of five-and six-membered A -alkylated lactams and lactones (eq 4 and 5). In both cases, 1 is first converted to the corresponding lithium amide and pre-complexed with lithium bromide. Furthermore, in the case of the lactams, it was observed that the use of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) as the solvent resulted in higher yields and greater enantiomeric excess. 

The subsequent transformation of these cycloadducts further illustrates the versatility of this approach in the construction of guaianolide sesquiterpenes (Scheme 1)7 The moiety incorporated in the adduct allows for the introduction of diverse functionalities at C-S and C-2. For example, reduction of the cycloadduct (11) with sodium borohydride produces a good yield of the iron complex (16). Oxidation of this complex with cerium ammonium nitrate gives methyl ester (17). In addition, (11) reacts with nucleophiles such as lithium dimethylmalonate and methanol to give the alkylated complex (18) and the meth-oxylated complex (19), respectively. Oxidative demetallation of (11) with bromine leads to selective replacement of the moiety at C-2 by bromide. ... 

Lithium iodide forms a solid complex with ammonia, Li(NH3)4l, but the related hydrate, alcoholate and amine complexes are less stable. These complexes presumably involve ion-dipole bonds (p. 115), the nitrogen lone pairs surrounding the Li+ some covalent character (dative bonding) is also permissible if s and p orbitals on the Li are invoked. The chloride, bromide and iodide of lithium are much more soluble in alcohol and ether than those of the other alkali metals, but this is not always a reliable indication of covalent character. The property is employed in separating lithium from sodium. 

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