Ethers complexes with organolithium

Conjugate addition of acyl groups to a,fl-unsaturated carbonyl compounds.3 Nickel carbonyl forms unstable complexes with organolithium compounds (ether,... 

It is of interest to note that Kminek, Kaspar and Trekoval have made calorimetric measurements on the interaction of n-butyllithium with several Lewis bases at RLi/base ratios of one. The largest enthalpy changes (in agreement which the results of Quirk and Kester were found for TMEDA and dimethoxyethane and the smallest with diethyl ether and anisole. Their results for anisole clearly show that even aromatic ethers will interact and complex with organolithium species. Thus, their findings serve to fortify the viscometric findings regarding the influence of aromatic ethers on the poly(styryl)lithium association state. 

The equatorial selectivity observed with organolithium reagents is enhanced in diethyl ether as the reaction solvent by the addition of lithium perchlorate (Table l)12. I3C-NMR studies47 indicate that the formation of a complex between lithium perchlorate and the carbonyl group, which also leads to a dramatic enhancement of the rate of the addition reaction, accounts for the increased diastereoselectivity. 

The organolithium species is generated by reaction of 4 with 2 eq. of tBuLi at -78 °C in ether. Acylation with M-methoxy-A-methylamide (Weinreb amide)15 5 forms the intermediate complex 22. 

The byproduct Li halide formed in reaction (a) is of no significance however, complexes of organolithiums with Li halides have reactivities different from salt-free organolithiums, and this can be important. Because LiCl is less soluble in ether than the bromide, low halide concentrations can be obtained in ether by using the organic chloride. 

White phosphorus also reacts with carbon nucleophiles in ether or tetrahydrofuran to give dark red solutions believed to be complex organophosphides (Rauhut and Semsel). Hydrolysis of a mixture obtained from reactions of white phosphorus with organolithium and organomagnesium compounds gives the primary phosphine as the major product, with small amounts of secondary and tertiary phosphines being formed under some conditions. 

B-Chloro-9-BBN, prepared readily from 9-BBN by treatment with dry hydrogen chloride in ether, reacts rapidly with organolithiums at -78 °C in n-pentane. The intermediate ate complex is not stable and breaks down to organoborane and lithium chloride even at -78 C (Chart 23.2) [1]. 

Allenylprostaglandin (295) is obtained by treatment of the acetate (296) with excess MegCuLi in ether at —78 C. The mechanism is complex, Reaction of 1,3-dialkoxyalk-l-ynes (297) with organolithium compounds affords a mixture of allenyl ethers (298) and 2-alkynyl ethers (299) the allenyl ethers (298) are converted into conjugated alkoxydienes (300) by acid-catalysed isomerization. ... 

The microstructure of the butadiene polymer in this system has been determined by infrared spectroscopy. The vinyl content shown in Table IV was 18 to 20 percent higher in the presence of crown ether than that observed with the n-butylsodium system alone. Thus, a steady increase in the crown ether concentration showed a moderate increase in the vinyl content (68 to 80 percent) at 30 C polymerization temperature. However, we did not observe the temperature dependence of vinyl content as is typical in the polymerization of 1,3-butadiene initiated with organolithium compounds modified by polar modifiers.36 Instead, we only observed a moderate change in the vinyl content. As can be seen in Table V, the vinyl content of polybutadiene prepared by n-butylsodium/tricyclohexyl-18-crown-6 initiator decreases only from 83 percent to 70 percent as the polymerization temperature increased from 30 C to 70 C, respectively. The relatively small change of vinyl content, or 1,2 content, of polybutadiene can be interpreted as the existence of a stable complex between the allylic anion and crown ether. This would lead to less dissociation than observed with simple ethers. Thus, the microstructure of the polymer would be less sensitive to temperature. 

This complex should be used when the organolithium is in solution in a hydrocarbon solvent. For organolithium reagents prepared in ether (see Note 4), the same complex may be used or, more conveniently, copper iodide (Cull can be used. The Cul purchased from Prolabo or Merck 4 Company, Inc. may be used directly. Other commercial sources of Cul (Fluka, Aldrich Chemical Company, Inc., Alfa Products, Morton/Thiokol, Inc.) furnish a salt which affords better results when purified. 1 mol of Cul is stirred for 12 hr with 500 ml of anhydrous tetrahydrofuran, then filtered on a sintered glass funnel ( 3), washed twice with 50 ml of anhydrous tetrahydrofuran, once with 50 ml of anhydrous ether and finally dried under reduced pressure (0.1 imO for 4 hr. 

Crystal structure determination has also been done with -butyllithium. A 4 1 n-BuLi TMEDA complex is a tetramer accommodating two TMEDA molecules, which, rather than chelating a lithium, link the tetrameric units. The 2 2 -BuLi TMEDA complex has a structure similar to that of [PhLi]2 [TMEDA]2. Both 1 1 -BuLi THF and 1 1 -BuLi DME complexes are tetrameric with ether molecules coordinated at each lithium (Fig. 7.2). These and many other organolithium structures have been compared in a review of this topic. ... 

The mechanism of organolithium addition to naphthyl oxazolines is believed to occur via initial complexation of the alkyllithium reagent to the oxazoline nitrogen atom and the methyl ether to form chelated intermediate 17. Addition of the alkyl group to the arena 7t-system affords azaenolate 18, which undergoes reaction with an electrophile on the opposite face of the alkyl group to provide the observed product 4. The chelating methyl... 

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). 

Elimination to yield alkenes can be induced thermally or by treatment with acids or bases (for one possible mechanism, see Figure 3.39) [138,206]. Less common thermal demetallations include the thermolysis of arylmethyloxy(phenyl)carbene complexes, which can lead to the formation of aryl-substituted acetophenones [276]. Further, (difluoroboroxy)carbene complexes of molybdenum, which can be prepared by treating molybdenum hexacarbonyl with an organolithium compound and then with boron trifluoride etherate at -60 °C, decompose at room temperature to yield acyl radicals [277]. 

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