Alkyl into alkyllithiums

Another possibility of transforming indirectly alcohols into alkyllithium compounds consists in nsing the corresponding sulfates. Alkyl sulfates 60 were lithiated using naphthalene (4%) as the electron carrier catalyst in THF at —78 °C yielding two equivalents of the corresponding alkyllithinm 61. Further addition of an electrophile at —78 to 0°C led to the formation, after hydrolysis, of the final prodncts 20 (Scheme 22) ... 

Atkyllithium reagents. This aromatic radical anion (1) is particularly effective for conversion of alkyl halides into alkyllithium reagents. These products are formed in 93-95% yield from reactions conducted in THF at — 78°. 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Additions of aryl- or alkyllithium reagents to N-silylated formamides 508 give the imines 509 in 55-80% yield [90, 91] some of these imines can subsequently be converted into the corresponding //-lactams by reaction with enolates of alkyl butyrates [92]. Conversion of N-silylated butyrolactam 388 into cyclic Schiff bases such as 390, by reaction with methyl- or butyllithium, via O-silylated butyrolactam 389, is discussed in Section 4.8 (Scheme 5.28). 

Metal alkyls can be prepared in a simple manner from the main group halides (X = Cl, Br, I) and the appropriate alkyl Grignard reagent (RMgl) or the alkyllithium salt (RLi), as shown for the cadmium alkyls (Equation (2)).13 The elimination of impurities from the precursor source is of great importance, as any remaining impurities are invariably carried over into the growing semiconductor layers. Incorporation of impurities, even at levels as low as 1015 free carriers per cubic centimeter (one part in ca. 107), can drastically affect the electronic properties of the... 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

Finally, a reaction that clearly shows the electrophihc carbenoid-type character of a-lithiated epoxides is the reductive alkylation discovered by CrandaU and Apparu. The transformation is illustrated by the treatment of f-butyl ethylene oxide with t-butyllithium to yield ii-di-f-butylethene (equation 55). The overall reaction results in a conversion of an oxirane into an aUcene under simultaneous substitution of an a-hydrogen atom by the alkyllithium reagent ... 

The kinetic effects of THF on alkyllithium has been clearly demonstrated. Morton, Bostick, Livigni and Fetters (44) have studied the polymerization of butadiene and isoprene using butyllithium in THF and in normal hexane. By using a preinitiation technique, the kinetics of the propagation could be determined. In all cases the rate of polymerization was proportional to the monomer concentration. In THF the rate of polymerization was proportional to the alkyl lithium concentration. However, in hexane the rate of polymerization was proportional to the square root of the lithium alkyl concentration. Morton et al. showed that the polymerization in hexane involved the dimer of the alkyllithium which dissociated into two alkyllithium molecules before propagating the polymerization. The THF adduct of the alkyllithium, however, was able to react directly. 

General procedure for the preparation of ketones from A,/V-dimethylcarbox-amides and alkyllithiums.127c A suspension of lithium ribbon (1.6g-atom), cut into small pieces, in anhydrous ether (800 ml) is prepared in a flask fitted with a reflux condenser, nitrogen inlet tube, thermometer, a pressure-equalising addition funnel and a stirrer. The suspension is cooled to — 10 °C, and, while the system is being swept with nitrogen, a solution of the required alkyl bromide (0.83 mol) in ether (200 ml) is added over a period of 2 hours. The mixture is stirred for 1 hour longer at — 10 °C. Then the temperature is lowered to — 20 °C and a solution of the required iV,jV-dimethylcarboxamide in anhydrous ether (200 ml) is added dropwise over a period of 1.5 hours. The... 

Addition of alkyllithium reagents to pseudoephedrine amides leads to the formation of enantiomerically enriched ketones (eqs 9 and 10). The protocol developed to transform alkylated pseudoephedrine amides into ketones was optimized to avoid premature breakdown of the tetrahedral intermediate generated following addition of the organolithium species to the amide. ... 

It has been shown that metallation of diisopropyl phosphates derived from primary aliphatic alcohols, except methanol, takes place at the alkyl as well as the isopropyl group in a ratio which is strongly influenced by steric effects. It was proposed that short-lived alkyllithium compounds were configurationally stable up to — 50°C and rearrange, with retention of configuration, into the corresponding a-hydroxyphosphonates (phosphate-phosphonate rearrangement) (Scheme 21). ... 

Alkyllithium compounds LiR react stoichiometrically with butadiene and isoprene in hydrocarbons to form the corresponding alkyl-substituted butenyllithium compounds. If the diene is applied in excess, the polymerization can be catalyzed by further diene insertion into the allyl-lithium bond. Both steps have been proved directly but the mechanism of the selectivity remains an open question [41, 42]. 

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. 

---