Dimethoxyethane reagents

Several reviews cover hetero-substituted allyllic anion reagents48-56. For the preparation of allylic anions, stabilized by M-substituents, potassium tm-butoxide57 in THF is recommended, since the liberated alcohol does not interfere with many metal exchange reagents. For the preparation of allylic anions from functionalized olefins of medium acidity (pKa 20-35) lithium diisopropylamide, dicyclohexylamide or bis(trimethylsilyl)amide applied in THF or diethyl ether are the standard bases with which to begin. Butyllithium may be applied advantageously after addition of one mole equivalent of TMEDA or 1,2-dimethoxyethane for activation when the functional groups permit it, and when the presence of secondary amines should be avoided. 

In related studies (S)-3-alkylcycloalkanones were obtained in moderate to high enantiomeric purity from the addition of dialkylmagncsium reagents to (,S)-2-(4-methylphenyl-sulfinyl)-2-cycloalkenones in dimethoxyethane at — 78 "C11. The addition of divinylmagne-sium and diphenylmagnesium occurred in the same stereochemical sense11. 

The enol acetates, in turn, can be prepared by treatment of the parent ketone with an appropriate reagent. Such treatment generally gives a mixture of the two enol acetates in which one or the other predominates, depending on the reagent. The mixtures are easily separable. An alternate procedure involves conversion of a silyl enol ether (see 12-22) or a dialkylboron enol ether (an enol borinate, see p. 560) to the corresponding enolate ion. If the less hindered enolate ion is desired (e.g., 126), it can be prepared directly from the ketone by treatment with lithium diisopropylamide in THE or 1,2-dimethoxyethane at —78°C. ... 

Figure 2.9. Synthesis of conditurol C Reagents and conditions i, E. coli JM109 (pDTGbOIA) ii, 2,2-dimethoxypropane, acetone, / -TsOH iii, 1,3-dibromo-5,5-dimethylhydantoin, H20-acetone iv, NaOH, H20-dimethoxyethane, heat v, e, MeCN, Et4NBr vi, NaOBz, H2O.

Niobium(III) chloride-Dimethoxyethane, NbCl3 DME (1). This soluble Nb(III) reagent is obtained as a brick-red solid by reduction of NbCl> in DME with Bu,SnH. 

Scheme 6.26. Construction of polyketide building blocks by sequential directed stereoselective hydroformylation and directed cuprate addition with the aid of the reagent-directing o-DPPB group. (o-DPPB = ortho-diphenylbenzoylphosphanyl, DME = dimethoxyethane)...

The use of KN(SiMe3)2 as metalating reagent enabled us to prepare the dimeric potassium derivative [(Cy7Si70i2)2Kg(DME)4] (18) as a crystalline solid, which was structurally characterized by X-ray diffraction (Scheme 7). Here again a box-shaped KgOg polyhedron forms the central structural unit. Four potassium ions are coordinated by DME (1,2-dimethoxyethane) ligands. ... 

Reduction of aromatic aldehydes to pinacols using sodium amalgam is quite rare. Equally rare is conversion of aromatic aldehydes to alkenes formed by deoxygenation and coupling and accomplished by treatment of the aldehyde with a reagent obtained by reduction of titanium trichloride with lithium in dimethoxyethane. Benzaldehyde thus afforded /ra/is-stilbene in 97% yield [206, 209]. 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

Cis-RuClj(phen)3 is made as black crystals by reaction of RUCI3 with (phen). As CM-RuCl2(phen)3/aq. yO / BuOH or 1,2-dimethoxyethane it stereospecifically epoxidised oleic acid to 9, 10-epoxyoctadecanoic acid [833] The reagent cis-RuCljlphey /aq. Li(C10)/CH3Cl2 oxidised dipropylether to propylpropionate, tet-rahycfiopyran to 6-valerolactone, adamantane to adamantan-l-ol and adamantanone, and octan-2-ol to octan-2-one [834],... 

To 2.05 g (10.0 mmol) of (-)-(4S, 5S )-4.5-dihydro-4-methoxymelhyl-2-mcthyl-5-phenyloxazole in 35 mL of 1,2-dimethoxyethane (N, — 78 X) are added dropwise 4.55 mL (10.5 mmol) of butyllithium (2.3 M in hexane) to produce a light yellow solution that is stirred ail additional. 30 min. Then 2.5 g (57 mmol) of oxirane are added ileat, in a stream, via a cannula from the septum-topped reagent bottle. The clear solution is slowly warmed from —78 to 0 C over a 6-h period. After the mixture is cooled back down to — 78 X, 1.4 mL (11 mmol) of chlorotrimethylsilane aTe added neat and the solution is allowed to warm to r.t. Most of the solvent is then removed on a rotary evaporator, the residue is taken up in hexane, and the insoluble matter is filtered off. Concentration and distillation gives the product as a clear oil yield 2.5 g (80%) bp 150 C/0.015 Torr [a]23 -41.6 (c = 9.8, c HCI3). 

A homogeneous solution of the bis(iodomethyl)zinc DME complex in dichloromethane can be prepared by adding diethylzinc to 1 equivalent of 1,2-dimethoxyethane in dichloromethane followed by 2 equivalents of diiodomethane . The presence of DME makes the preparation of the reagent safer by ensuring that the mixture is constantly homogeneous. This reagent has been useful in enantioselective cyclopropanation reactions vide infra). 

Use of more efficient solvents (tetrahydrofuran, isopropyl ether, dimethoxyethane) or more soluble metal hydride reagents (sodium borohydride, lithium tributoxy aluminum hydride, sodium bis(2-methoxyethyl) aluminum hydride) favors the alternative reduction pathway to the hydroquinone. 

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