Lithium r-butoxide

The selenium-stabilized carbanions derived by deprotonation of selenoacetals by strong bases, such as a mixture of KDA-lithium r-butoxide, LiTMP in HMPT/THF or LBDA in THF at -78 °C, react readily with a variety of electrophiles including primary or secondary halides, epoxides, ketones, aldehydes and enones, followed by deprotection, to give ketones, 3-hydroxy ketones, a-hydroxy ketones and 1,4-dicarbonyl compounds respectively. - - ... 

Kuwajima and coworkers used very hindered bases such as (2) to deprotonate methyl alkyl ketones regioselectively in the presence of enolizahle aldehydes.One example of this amazing process is shown in equation (11) the reaction is reported to work equally well with other methyl ketones, including 2-pentanone. The process was also demonstrated with other bases in the reaction of 3-methyl-2-buta-none with dihydrocinnamaldehyde (equation 12). Among the bases that are effective are LDA, lithium hexamethyidisilazane, lithium r-butoxide and even lithium ethoxide. However, base (2) is superior, giving the aldol in 83% yield. 

Oxidation of alcohols. In a new method for oxidation of primary and secondary alcohols to aldehydes and ketones, respectively, the alcohol is converted into an alkoxymagnesium bromide by reaction with ethylmagnesium bromide in THF at 20° a solution of lithium r-butoxide (2.4 eq.) is added and then, after 1 hr., NCS (2.4 eq.) is added. The suspension is stirred for 1 hr. 

Lithium bis(trimethylsilyl)amide, 542 Lithium r-butoxide, 115, 116, 118 Lithium r-butylmercaptide, 343, 344 Lithium a-carboethoxyvinyl(l -hexenyl)-cuprate, 329-330... 

Evidence for the existence of a single electron transfer mechanism for the benzilic ester rearrangement of benzil and 9,10-phenanthrenoquinone in the presence of lithium r-butoxide in tetrahydrofuran-benzene mixture was reported by Screttas et al They showed that the reaction with lithium t-butoxide occurred cleanly, while the usage of other alkoxides such as LiOEt... 

Note Yields in parentheses are under the previously published conditions using lithium r-butoxide. 

With higher homologs e.g., propynyl, butynyl), 3j5-hydroxyandrost-5-en-17-one does not react well with the alkyne and potassium r-butoxide, or with the lithium alkyne in tetrahydrofuran. However, satisfactory results are obtained by use of the alkynylmagnesium bromide in tetrahydrofuran, ... 

Hindered lithium dialkylamides can generate aryl-substituted carbenes from benzyl halides.162 Reaction of a,a-dichlorotoluene or a,a-dibromotoluene with potassium r-butoxide in the presence of 18-crown-6 generates the corresponding a-halophenylcarbene.163 The relative reactivity data for carbenes generated under these latter conditions suggest that they are free. The potassium cation would be expected to be strongly solvated by the crown ether and it is evidently not involved in the carbene-generating step. 

Allyltriphenylsilane, 13 Diacetatobis(triphenylphosphine)-palladium(II), 91 Dichlorobis(triphenylphosphine)-palladium(II), 103 (3-Dimethylaminopropyl)triphenyl-phosphonium bromide, 119 Lithium diisopropylamide-Potassium r-butoxide, 164... 

Reductive cleavage of cyclic ethers This complex is effective for reductive cleavage of cyclic ethers. The order of reactivity is epoxide > oxetane > tetrahydrofurane>tetrahydropyrane>oxepane. It is less effective for cleavage of acyclic ethers, except for methyl ethers. The reaction involves formation of a complex of the ethereal oxygen with aluminum r-butoxide followed by Sn2 displacement with lithium triethylborohydride. Steric and electronic Victors are involved, but yields are >90% in favorable cases. 

The intramolecular Claisen condensation of the dimeric model (22, R = Me) of PMMA was observed during NMR analysis, even at low temperature. This condensation results in the formation of a cyclic /3-keto ester (23), methyl 2-lithioisobutyrate and lithium f-butoxide (equation 26). 

DIENES Dichloromalcic anhydride. DITERPENES Palladium catalysts. OLEFINS Cuprous chloride. Lithium di-phenylphosphide. Lithium orthophosphate. Potassium r-butoxide. Thiophe-nol-Azobuty toni tide. OXASPIROPENTANE Lithium iodide. 

Alkali metal salts with nucleophilic anions are notably good initiators for chloral anionic polymerization (Fig. 26). The most studied initiator is lithium ferf-butoxide. When 0.2 mole % of lithium ferf-butoxide (based on chloral) was added to neat chloral monomer at 60°C the alkoxide (CH3)3C0CH(CCl3)0 Li was formed instantaneously, but no further addition of chloral occurred. This reaction was observed by an NMR study of the system and confirmed by the chemical reactions of the product alkoxide, which acted as the initiator. Tertiary amines such as pyridine and NR3 where R is an alkyl group have been found to be good initiators for chloral polymerization. They are slower initiators than lithium... 

Another mixed aggregate complex consisting of Bu°Li and r-butoxide was reported in 1990 as the tetramer (45). Hiis complex was first isolated by Lochmann and has been shown to be tetrameric and dimeric in benzene and THF, respectively, by cryoscopic measurements, and it has also been studied by rapid injection NMR techniques. Hiis species has received much attention because it is related to the synthetically useful superbasic or LiKOR reagents prepared by mixing alkali metal alkoxides with lithium alkyls or lithium amides. ... 

This discussion of aliphatic carbanion structures has included mainly organolithium compounds simply because the structures of most aliphatic caibanions incorporate lithium as the counterion and also because this alkali metal cation is the most widely used by synthetic organic chemists. For comparison the entire series of Group la methyl carbanion structures, i.e. MeNa, MeK, MeRb and MeCs, have been determined. Methylsodium was prepared by reaction of methyllithium with sodium r-butoxide. Depending upon the reaction conditions, the products obtained by this procedure contain variable amounts of methyllithium and methylsodium (Na Li atom ratios from 36 1 to 3 1). Hie crystal structure of these methylsodium preparations resembles the cubic tetramer (38) obtained for methyllithium with the Na— Na distances of 3.12 and 3.19 A and Na—C distances of 2.58 and 2.64 A. 

In Homer s original work, phosphine oxides (202) were treated with potassium r-butoxide or sodamide and allowed to react with an aldehyde or ketone to form the alkene (203) directly (Scheme 28). Homer observed that the use of a lithium anion resulted in the isolation of Ae p-hydroxyphosphine oxide (204). In addition, he found that the intermediate hydroxyphosphine oxide could be obtained by LAH reduction of the ketophosphine oxide. Warren and coworkers t ve utilized and expanded upon these techniques by isolating and separating the diastereomeric, frequently crystalline, p-hydroxyphosphine... 

Bromination of an olefin and double dehydrobromination of the resulting 1,2-dibromide is a classical method for the generation of 1,3-dienes (Table 1). Bromination of a double bond can be done with molecular bromine or, more conveniently, with pyridinium bromide perbromide . A variety of bases has been employed for dehydrobromination. While potassium hydroxide and sodium methoxide have been used for a long time, lithium carbonate-lithium chloride in DMF or hexamethylphosphoric triamide (HMPA) works well in many cases . Double dehydrobromination with hindered bases such as potassium r-butoxide or diazabicyclononene (DBN) and diazabicycloundecene (DBU) give good results. 

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