Lithium phenoxide

Similar information is available for other bases. Lithium phenoxide (LiOPh) is a tetramer in THF. Lithium 3,5-dimethylphenoxide is a tetramer in ether, but addition of HMPA leads to dissociation to a... 

Macomber, R. S. et al., Synth. React. Inorg. Met.-Org. Chem., 1977, 7, 111-122 The dried solid product from interaction of lithium phenoxide and silver perchlorate in benzene (probably largely silver phenoxide) exploded on gentle heating. Other silver alkoxide derivatives were unstable. 

Cyclopentenone annelation. The reaction of the dilithio derivative (2) of dimethyl 4-cyclohexene-1,2-dicarboxylate (LDA, THF/HMPT) with 1 at -45 -> 0° results in the bicyclic enone 3 in 72% yield. The reaction may involve conjugate addition of 2 to 1 to give a ketene (a) with loss of lithium phenoxide. Several other... 

The cyclic sulfites were first found to react with lithium phenoxides as nucleophiles in DMF in a one-pot procedure commencing from the unprotected diol [357]. Subsequent work opened up this class of donor to alcohol nucleophiles in conjunction with the use of a Lewis add, such as Yb(OTf)3 or Ho(OTf)3, to activate the donor in refluxing toluene (Scheme 4.57) [314,358,359]. The very high degree of P-selec-tivity observed in these reactions is consistent with an SN2-like displacement of the sulfite oxygen. 

In the late 1960s, methods were developed for the synthesis of alkylated ketones, esters, and amides via the reaction of trialkyl-boranes with a-diazocarbonyl compounds (50,51), halogen-substituted enolates (52), and sulfur ylids (53) (eqs. [33]-[35]). Only one study has addressed the stereochemical aspects of these reactions in detail. Masamune (54) reported that diazoketones 56 (Ri = CH3, CH2Ph, Ph), upon reaction with tributylborane, afford almost exclusively the ( )-enolate, in qualitative agreement with an earlier report by Pasto (55). It was also found that E) - (Z)-enolate isomerization could be accomplished with a catalytic amount of lithium phenoxide (CgHg, 16 hr, 22°C) (54). 

The reaction of lithium phenoxide with cirmamyl methyl carbonate at 50 °C gave excellent selectivities, if the reaction time was less than about 20 h. However, longer reaction times led to a fall in both regioselectivity and enantioselectivity, which indicated that the reaction is reversible. 

An indirect oxidimetric titration method for alkylhthium compounds may be carried out, taking advantage of the fact that vanadium pentoxide causes fast and complete oxidation of alkyllithiums in solution. After the end of this reaction the reduced vanadium compounds are dissolved in sulfuric acid and titrated with Ce(IV) sulfate, using as indicator Ee(II) and 1,10-phenanthroline (64) sulfate. This method is inadequate for aryllithium compounds because the lithium phenoxide impurities reduce vanadium pentoxide. ... 

The lithium phenoxide may be prepared in larger quantities and may be stored for some time sealed under nitrogen and protected from light by wrapping the flask with aluminum foil. Traces of water lead to a gummy salt, while traces of oxygen cause a purple coloration. Quite badly discolored salt has been used successfully in the alkylation procedure, but yields tend to be reduced by tar formation. 

However, a careful study of the experimental data has led to some general trends. For instance, the nature of the final products depends heavily on the alkali cations used in the starting compounds sodium and lithium phenoxides reacting under similar experimental conditions yield the related salicylates as major products [18] (Scheme 5.1), whereas potassium, rubidium, and cesium phenoxides yield mixtures of 2-hydroxy-benzoic acid and 4-hydroxy-benzoic acid [1] (Scheme 5.2). As a rule of thumb, the yield of p-hydroxybenzoic acid generally increases with the increasing ionic radius of the alkali metal. Both, temperature and C02-pressure were also reported to be paramount in the selectivity of the carboxylation ... 

The cleavage of anisole to lithium phenoxide by lithium in refluxing THF in the presence of biphenyl has been known since 1961,4142 and in 1963 Eisch published a practical method for forming allyllithium 32 from allyl phenyl ether 31, again using lithium in the presence of biphenyl, but at 0 °C or below.43 Twelve equivalents (a six-fold excess) of lithium metal was required for good yields in this reaction. A similar reaction takes place between benzyl phenyl ether and lithium.44... 

Diastereoselective synthesis of p-substituted a-hydroxyphosphinates (252) and (253) by hydroxyphosphinylation of a-silyloxy aldehydes (254) and a-amino aldehydes (255) with ethyl allylphosphinate (256), catalysed with lithium phenoxide, has been reported (Figure 47). ... 

Similar information is available for other bases. Lithium phenoxide (LiOPh) is a tetramer in THF. Lithium 3,5-dimethylphenoxide is a tetramer in ether, but addition of HMPA leads to dissociation to a monomer. Enolate anions are nucleophiles in reactions with alkyl halides (reaction 10-68), with aldehydes and ketones (reactions 16-34, 16-36) and with acid derivatives (reaction 16-85). Enolate anions are also bases, reacting with water, alcohols and other protic solvents, and even the carbonyl precursor to the enolate anion. Enolate anions exist as aggregates, and the effect of solvent on aggregation and reactivity of lithium enolate anions has been studied. The influence of alkyl substitution on the energetics of enolate anions has been studied. ... 

Scheme 350 shows the structures of a number of mono-Cp titanium complexes with more elaborately substituted aryloxo ligands. The compounds are formed by the reaction of Cp TiCl3 with 1 equiv. of the substituted phenol in the presence of an excess of pyridine or by treatment of the lithium phenoxide with Cp TiCl3 some of them have been... 

An elegant photochemical formation of an aryl-carbon bond through a PET mechanism was recently reported in the total synthesis of the potent antimitotic polycycle (-)-diazonamide A. The reaction was initiated by intramolecular electron transfer between the indole chromophore and the adjacent bromoarene (Scheme 2.10). Thus, compound 21 was treated with an aqueous-acetonitrile solution of LiOH and the resulting lithium phenoxide solution was degassed and photolyzed (Rayonet, 300 nm) to yield biaryl 22 (as a single atropodiastereomer) in a good yield. A radical-radical anion pair (23) was formed upon excitation, and... 

Phenoxide ion, unlike alkoxides, interacts favorably with alkynyliodonium species. Reaction of two equivalents of lithium phenoxide with the [bis(phenyliodonium)ethyne, 30, results in diphenoxyacetylene, 79 [24] [Eq. (36)]. Benzofurans, 81, are obtained in the reaction of 23 with PhONa in methanol [Eq. (37)] [64]. As indicated, these products arise via insertion of the intermediate carbene, 80, into the ortho-C-H bond. 

A particularly interesting mixed-metal polymer was synthesized from the metallocene 19. This reaction (Scheme XV) was conducted by first converting the phenol functionalities of 19 to lithium phenoxides via reaction with methyl lithium. Subsequent reaction with (ri -C5H5)2ZrCl2 gave the desired polymeric product. Detailed studies of the physical and chemical properties of this polymer are currently in progress. 

Considerable effort has been made in developing iV-diphenylphosphinoyl (Dpp) aid- and keto-imines as electrophilic partners in copper-catalyzed 1,2-additions (Scheme 1-10). Thioamides and aldimines e.g., 123) in the presence of a soft Lewis acidic Cu(I) salt complexed by 6/5-phosphine 124, together with a hard base in the form of a lithium phenoxide, react to afford products in good-to-excellent ee s. Activation resulting from a likely Cu-S interaction increases the acidity of an a-proton and, hence, more facile deprotonation. With alkyinitriles as nucleophiles generated via an initial decarboxylative process e.g., from 125), a DTBM-SEGPHOS-coordinated copper complex arrives at C-C bond formation in usually >80% ee. 

Tamao-Corriu coupling the effectiveness of DHTP over HTP can also be attributed to the increased probability for the lithium phenoxide moiety to be situated close to the palladium. 

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