Reactions lithium aryls

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

The B-B bonded l,2-dimethoxydiborane(4) precursor67 was selected on the basis that it could be obtained readily from (MeO)2B-B(OMe)268 by reaction with the lithium aryl. In contrast to diborane(4) tetrahalides,... 

In principle, each of the above protodelithiation reactions is in equilibrium. It is clear that, in practice, they are not. The protonating species, HBr, isopropanol and 2-butanol, are simply too acidic for the reaction to be reversible. Although the hydrogen/lithium exchange equilibria cannot be smdied in both directions, halogen/Uthium exchange reactions with aryl substituents evidently are true equilibrium processes. Winkler and Winkler studied reaction 11 (among others), in either diethyl ether or in THF at 25 °C. 

Concerning the lithium-zinc transmetallation from intermediate 331, it has been used (THF, room temperature) to perform a palladium-catalyzed Negishi cross-coupliug reaction with aryl bromides - and a 8 2 regioselective allylation in the presence of copper cyanide. 346 and 347 were, respectively, obtained (Scheme 101). 

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

The lithium derivatives of 1-substituted pyrroles and indoles provide another general route of access to 2-acyl pyrroles and indoles. The ketones can be obtained directly by reaction with aryl nitriles or acid halides but, at least for 1-benzenesulfonylindole, a two-step procedure involving reaction with an aldehyde followed by oxidation of the carbinol to the ketone is frequently more convenient (equation 179) (73JOC3324, 75JOC2613). This method is probably the most general route to 2-acylindoles, although many have also been prepared by direct Fischer cyclization (see Section 3.06.3.4.2). 

Cossio and Linden et al. studied the reaction of aryl iminoester-derived azomethine ylides 65 with 2- and 1,2-disubstituted nitroalkenes 66 using silver acetate and triethylamine in acetonitrile (Scheme 2.18).35 The product 3-nitropyrrolidines were formed in yields of 24—69% with excellent regioselectivity. These findings mirrored earlier work by Toke et al.36 Unfortunately, diastereoselectivity was generally in the 1 1—4 region. Only in two cases where yields were low were the products formed in a 2 98 ratio. Lithium perchlorate was able to catalyze the reaction as well with similar yields. Remarkably, the diastereoselectivity with lithium perchlorate in some cases resembled that obtained with silver acetate and in others was reversed. Cossio also reported the stereoselective reaction of phenyl isocyanates with azomethine ylides 65 under the same conditions.37 These reactants combined to give the expected products as single stereoisomer in 30-50% yield. 

The University of Kyoto, Japan, reports about a halogen-lithium exchange reaction of aryl bromides with butyl lithium (see Figure 5.20) [53,57]. The intermediate was trapped with an electrophile. The whole process was done under noncryogenic conditions at 0°C. 

Carbolithiation proved to be a very effective approach to highly cytotoxic titanocenes. The reaction of aryl or heteroaryl lithium species with 6-/V,/V-d i me thy I am i n o fulvene and subsequent transmetallation reaction led to dimethylamino-functiona-lised titanocenes with IC50 values of 6.8, 5.5 and 5.4 pM. Furthermore, this reaction proved to be tolerant to many substituents and to be a versatile tool for the synthesis of a wide variety of substituted titanocene dichlorides as seen in Scheme 3. 

Sodium benzenetellurolate is arylated in liquid ammonia via photoinduced reactions with aryl halides3,4. Aryl iodides reacted with sodium benzenetellurolate in the presence of copper(I) iodide in hexamethylphosphoric triamide (but not in DMF or DMSO) to produce aryl phenyl tellurium compounds5- However, lithium benzenetellurate reacted with 1,2-bromoiodobenzene and lithium methane tellurolate with 1,2-dibromobenzene in tetrahydrofuran at 20° to yield l,2-bis[organotelluro]benzenes6. 

Ham and coworkers85 have developed a one-pot synthetic method for the formation of aryl-alkyl sulfides, 94, from various alkyl halides and lithium aryl thiolates 93, which are prepared in situ from 92 formed by lithium—halogen exchange of 91, employing n-butyllithium (Scheme 31). The method avoids the use of unstable arylthiols and a catalyst is not required. Several aryl bromides were successfully employed in the reaction, and the corresponding sulfides were obtained in 71 to 96% yields. 

An example prepared by tin-lithium transmetallation is compound 637, which reacts with enolizable ketones, after transmetallation with cerium(III) chloride895. This intermediate was transformed into the corresponding vinylzinc reagent and, after palladium(O)-catalyzed cross-coupling reactions with aryl iodides, was used in the synthesis of the antitumor antibiotic rineomycinone B2 methyl ester940,941. The vinyllithium 627 has also been transformed into the corresponding vinyl iodide by stannylation followed by reaction with iodine. The arylation has been performed in this case by a palladium(0)-catalyzed... 

The alkyl can be collected by sublimation or distillation in a vacuum. On the other hand, the aryls are made by reaction of a lithium aryl in a hydrocarbon with BeCl2 in diethyl ether ... 

After this short digression to non-arylated phenoxenium ions we now return to the reactions of arylated stable phenoxenium salts 14a-c which are strong oxidants. When the dark blue solution of 14c in acetonitrile is mixed with the lithium salt of its phenol, the red 2,4,6-aryl triphenylphenoxyls immediately arises. 

The reaction of strong bases with aryl halides results in the generation of an aryne through loss of HX, Arynes can also be formed by reaction of aryl halides with lithium and organolithium compounds. 

Scheme 45. C-glycoside synthesis by reaction of sugar lactones with lithium aryls [ 137]...

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