Solvents hexamethylphosphoramide

Reaction of Z-a./j-unsaturated iron-acyl complexes with bases under conditions similar to those above results in exclusive 1,4-addition, rather than deprotonation, to form the extended enolate species. However, it has been demonstrated that in the presence of the highly donating solvent hexamethylphosphoramide, y-deprotonation of the -complex 6 occurs. Subsequent reaction with electrophiles provides a-alkylated products such as 736 this procedure, demonstrated only in this case, in principle allows access to the a-alkylatcd products from both Z- and it-isomers of a,/j-unsaturated iron-acyl complexes. The hexamethylphosphoramide presumably coordinates to the base and thus prevents precoordination of the base to the acyl carbonyl oxygen, which has been suggested to direct the regioselective 1,4-addition of nucleophiles to -complexes as shown (see Section 1.1.1.3.4.1.2.). These results are also consistent with preference for the cisoid conformations depicted. 

Solvents and counterions greatly influence the rate of reductive cleavage. The rate increases with decreasing polarity of the solvent and increasing size of the counterion these are the conditions that favor tight ion pairs, which disproportionate to dianions to a greater degree than loose ones. In the solvent hexamethylphosphoramide (HMPA) in which virtually all ion pairs are dissociated into free ions, the anion radical [NN] is stable. 

It is also seen in Figure 15 that the second requirement is satisfied displacements of the data points for HBA solvents from the regression line all reflect lower transition energies for the HBD solute 1, and range from 2.4 standard deviations of Equation 43 for the very weak HBA solvent trichloroacetone to 17.5 calculated from,... 

As an example, ferf-butyl (45)-l-methyl-2-oxoimidazolidine-4-carboxylate was used by Nunami and colleagues as a chiral auxiliary for DKR of a-bromo-carboxylic acids. In this case, the nucleophile was a malonic ester enolate and the role of the polarity of the solvent (hexamethylphosphoramide, HMPA) was demonstrated (Scheme 1.2). The alkylated products were further easily converted to chiral a-alkylsuccinic acid derivatives and chiral jS-amino acid derivatives. Moreover, these authors showed that this methodology could be extended to other nucleophiles such as amines." Therefore, the reaction of a diastereomeric mixture of tert-bvAy (45)-l-methyl-2-oxoimidazolidine-4-carb-oxylate with potassium phthalimide predominantly afforded fcrf-butyl (45)-1-methyl-3-((25)-2-(phthaloylamino)propionyl)-2-oxoimidazolidine-4-carboxylate in 90% yield and 94% diastereomeric excess (de). The successive removal of the chiral auxiliary afforded A-phthaloyl-L-alanine. 

The kinetics of the Menshutkin reaction of pyridine with benzyl bromide in methanol, acetone, and acetonitrile have been studied. " Second-order rate constants for the reactions of ethyl a-haloacetate and triethylamine have been determined in aprotic dipolar ketonic and halogenated solvents, nitrogen-containing solvents, and alcoholic solvents at 30 °C. Simple and multiple regression on various solvent parameters was applied to the results. The same group made a similar study of the reactions of ethyl a-haloacetate with triethylammonium carboxylates in a wide range of protic and aprotic solvents. The kinetics of alkylation of sodium acetate by butyl bromide have been investigated in dipolar non-hydroxylic solvents. Hexamethylphosphoramide is the best solvent for this reaction. 

Technora. In 1985, Teijin Ltd. introduced Technora fiber, previously known as HM-50, into the high performance fiber market. Technora is based on the 1 1 copolyterephthalamide of 3,4 -diaminodiphenyl ether and/ -phenylenediamine (8). Technora is a whoUy aromatic copolyamide of PPT, modified with a crankshaft-shaped comonomer, which results in the formation of isotropic solutions that then become anisotropic during the shear alignment during spinning. The polymer is synthesized by the low temperature polymerization of/ -phenylenediamine, 3,4 -diaminophenyl ether, and terephthaloyl chloride in an amide solvent containing a small amount of an alkaU salt. Calcium chloride or lithium chloride is used as the alkaU salt. The solvents used are hexamethylphosphoramide (HMPA), A/-methyl-2-pyrrohdinone (NMP), and dimethyl acetamide (DMAc). The stmcture of Technora is as follows ... 

The polyamides are soluble in high strength sulfuric acid or in mixtures of hexamethylphosphoramide, /V, /V- dim ethyl acetam i de and LiCl. In the latter, compHcated relationships exist between solvent composition and the temperature at which the Hquid crystal phase forms. The polyamide solutions show an abmpt decrease in viscosity which is characteristic of mesophase formation when a critical volume fraction of polymer ( ) is exceeded. The viscosity may decrease, however, in the Hquid crystal phase if the molecular ordering allows the rod-shaped entities to gHde past one another more easily despite the higher concentration. The Hquid crystal phase is optically anisotropic and the texture is nematic. The nematic texture can be transformed to a chiral nematic texture by adding chiral species as a dopant or incorporating a chiral unit in the main chain as a copolymer (30). 

Using hexamethylphosphoramide as the solvent, only the second reaction occurs. Disilane also reacts with potassium in 1,2-dimethoxyethane to form KS1H3, although S1H4 and nonvolatile polysHanes are also produced (28,31). Pure crystalline KSiH prepared from SiH and potassium in 1,2-dimethoxyethane has been obtained by slow evaporation of the solvent. WhenHquid ammonia is used as the solvent, only a small fraction of SiH is converted into metal salt most of the SiH undergoes ammonolysis (32). 

The degradation of VDC polymers in nonpolar solvents is comparable to degradation in the soHd state (101,125,129,130). However, these polymers are unstable in many polar solvents (131). The rate of dehydrochlorination increases markedly with solvent polarity. In strongly polar aprotic solvents, eg, hexamethylphosphoramide, dehydrochlorination proceeds readily (129,132). This reaction is cleady unlike thermal degradation and may well involve the generation of ionic species as intermediates. 

When hexamethylphosphoramide, (NMe2)3PO, is used as solvent only the second reaction occurs. The synthetic utility of KSiHa can be gauged from Table 9.7 which summarizes some of its reactions. In addition, PCI3 gives polymeric (PH) t, CO2 gives CO plus HCO2K (formate), and N2O gives N2 + H2 (plus) some Sifli in each... 

A highly explosive red/orange solid, obtained from rhenium trioxide and hydrogen peroxide reacting in hexamethylphosphoramide as solvent, was tentatively assigned this structure. 

Where the mercuric salt was formed in situ, the decomposition was effected in boiling water (e.g., Ref. 90). Where the preformed mercuric salt was used, the solvent was hexamethylphosphoramide (91). 

Miconazole nitrate was prepared by Godefori and co-workers [5-7]. Imidazole 1 was coupled with brominated 2,4-dichloroacetophenone 2 and the resulting ke-tonic product 3 was reduced with sodium borohydride to its corresponding alcohol 4. The latter compound 4 was then coupled with 2,4-dichlorotoluene by sodium borohydride in hexamethylphosphoramide (an aprotic solvent), which was then extracted with nitric acid to give miconazole nitrate. 

Diphenylmethane reacts with dioxygen in the presence of potassium 1,1-dimethylethoxide in various solvents (dimethylformamide [DMF], hexamethylphosphoramide [HMPA], pyridine) to produce nearly 100% yields of benzophenone [284]. The adduct of benzophenone with dimethylsulfoxide (DMSO) [l,l-diphenyl-2-(methylsulfinyl)ethanol] is formed as the final product of the reaction. The stoichiometry of the reaction and the initial rate depends on the solvent (conditions 300 K, [Ph2CH2] = 0.1mol L [Me3COK] = 0.2mol L 1,p02 = 97kPa). 

To test the validity of this mechanism, chromium carbonyl (1.0 g) was photolyzed under Ar at ambient temperature in a solution of methanol and hexamethylphosphoramide in the apparatus shown in Figure 5. The lamp was turned off periodically to check for the disappearance of slightly soluble Cr(C0) . Several photolyzing cycles were necessary to effect nearly complete conversion to the solvent-stabilized coordinately unsaturated species (equivalent to in Figure 4),... 

Kemp et al., 1978). The rate is slowest in an aqueous solution and is enhanced in aprotic and/or dipolar solvents. The rate augmentation of 106—108 is attainable in dipolar aprotic solvents such as dimethyl sulfoxide and hexamethylphosphoramide (HMPA). Interestingly, the decarboxylation rate of 4-hydroxybenzisoxazole-3-carboxylate [53], a substance which contains its own protic environment, is very slow and hardly subject to a solvent effect (1.3 x 10-6 s-1 in water and 8.9 x 10-6 s-1 in dimethylformamide Kemp et al., 1975). The result is consistent with the fact that hydrogen-bonding with solvent molecules suppresses the decarboxylation. 

We have recently reported ( ) several synthetic studies of weak nucleophile SnAr reactions. In the latter cases (26f-1), new synthetic methodology was reported for the direct introduction of fluoroalkoxy groups into a variety of aromatic systems. These reports represent synthetically useful procedures for obtaining some otherwise inaccessible fluoroalkoxy materials but, unfortunately, they require the use of a dipolar, aprotic solvent (usually hexamethylphosphoramide, HMPA) and, in some cases, elevated temperatures. However, because of their diverse and important applications ( ), the syntheses of these and other organofluoro compounds continue to be of interest. For example, two recent reports of useful fluoroalkoxy materials include the insecticide activity exhibited by fluoroalkoxy substituted 1,3,4-oxadiazoles... 

The reduction of an isolated carbon-carbon double bond by other methods is exceptional. Occasionally an isolated double bond has been reduced elec-Irolylicolly 344 and by dissolving melols. Sodium under special conditions -using tert-butyl alcohol and hexamethylphosphoramide as solvents - reduces alkenes and cycloalkenes in 40-100% yields [345. 3-Methylenecholestane, for example, afforded 3-methylcholestane in 74% yield on heating for 2 hours at 55-57° with lithium in ethylenediamine [346]. 

Hexamethylphosphoramide, which is a liquid under ambient conditions, is able to solvate electrons. Mixtures of this solvent with up to 21 % ethanol are effective for the electrochemical Birch type reactions. The strong hydrogen bonding between the two solvents suppresses hydrogen evolution at die cathode [42], Benzene is reduced at constant current in this solvent to a mixture of hydrocarbons, cyclohexane being formed early in the process [43,44],... 

A term, usually referring to a solvent, describing a compound which act neither as a proton donor nor a proton acceptor. Examples of polar aprotic solvents include dimethylformamide, dimethylsulfoxide, acetone, acetonitrile, sulfur dioxide, and hexamethylphosphoramide. Examples of nonpolar aprotic solvents include benzene and carbon tetrachloride. Studies of reactions in protic and aprotic solvents have demonstrated the importance of solvation on reactants, leaving groups, and transition states. Degrees of nucleophilicity as well as acidity are different in aprotic solvents. For example, small, negatively charged nucleophiles react more readily in polar aprotic solvents. It should also be noted that extremely... 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

The synthesis of 168 has also been completed by using other reaction conditions (Scheme 22). 6,7-Dimethoxyisoquinoline (162) was reacted with potassium cyanide and 2-chloromethylbenzoyl chloride in the presence of a catalytic amount of benzyltriethylammonium chloride, resulting in 164 which on treatment with lithium diisopropylamide in hexamethylphosphoramide-tetrahydro-furan solvent mixture afforded the cyclized product 168 in high yield (40). 

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