Hexamethylphosphoramide reactions

Lithium/hexamethylphosphoramide Reactions with alkali metals in hexamethylphosphoramide Reductive N-alkylation of azo compounds... 

Sulfur/hexamethylphosphoramide Reactions with sulfur in hexamethylphosphoramide Stilhenes... 

Other Reactions. Primary amyl alcohols can be halogenated to the corresponding chlorides by reaction with hydrogen chloride in hexamethylphosphoramide (87). Neopentyl chloride [753-89-9] is formed without contamination by rearrangement products. A convenient method for preparing / f/-amyl bromide and iodide involves reaction of / f/-amyl alcohol with hydrobromic or hydroiodic acid in the presence of Li or Ca haUde (88). The metal haUdes increase the yields (85 —95%) and product purity. 

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. 

In 1973 Du Pont commenced production of another aromatic polytunide fibre, a poly-(p-phenyleneterephthalamide) marketed as Kevlar. It is produced by the fourth method of polyamide production listed in the introductory section of this chapter, namely the reaction of a diamine with a diacid chloride. Specifically, p-phenylenediamine is treated with terephthalyl chloride in a mixture of hexamethylphosphoramide and V-methylpyrrolidone (2 1) at -10°C Figure 18.32). 

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... 

Hexamethylphosphoramide, S -2 reaction and. 371 Hexane, 1R spectrum of. 424 mass spectrum of, 413 1,3,5-Hexatriene, molecular orbitals of, 1180... 

Hexamethylphosphoramide Hoffmann, Roald, 1180 Hoffmann-I.a Roche Co., vitamin C synthesis and, 773 von Hofmann. August Wilhelm, 933 Hofmann elimination reaction. 936-938... 

Heterocyclic nitrogen donors and their adducts with zinc chloride have been studied.623,624 A large number of other ligand systems have also been characterized, for example, zinc halide adducts of 2,2-dimethylpropane-1,3-diamine and hexamethylphosphoramide have been studied.625,626 The formation of mixed ligand complexes with chloride and substituted pyridines has been studied.627 The zinc tris(pyridyl) chloride anion has also been structurally characterized.628 Manganese(II) ions have been used to probe the stereochemistry in reactions of zinc halides with pyrazine.629... 

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). 

This method does not allow the formylation of aliphatic Grignard or organolithium reagents since in these cases the enhancement in base strength in the presence of hexamethylphosphoramide produces side reactions due to proton abstraction. 

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... 

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). 

Ni[R-dtp]2 complexes form paramagnetic five-co-ordinate adducts with hexamethylphosphoramide Xo date no phosphate esters have been found to form adducts. However, the NMR spectra of solutions of Ni(R-dtp>2 complexes after long standing or gentle heating clearly show that scrambling reactions of the type ... 

Tetrahydro-l,4-oxazin-2-ones can be deprotonated and then reacted with electrophiles. Thus, for example, the nonlabeled analog of compound 81 was deprotonated at the 3-position with sodium hexamethyldisilazide and ethylated using ethyl iodide. The reaction was performed in a 1 10 mixture of hexamethylphosphoramide (HMPA) and tetrahydrofuran <1998T10419>. If a dihalide is used and the oxazine has a free 4-nitrogen, cycloalkylation can be achieved as shown in the reaction of 219 to give 220 (Equation 17) <1993LA477>. 

Synthesis of 2,3-dihydro-l,4-dithiin 11 was accomplished from l,3-dithiol-2-one 247 in the presence of dibro-moethane and potassium hydroxide <1998JOG3952>, while reaction of 2,3-dichloro-l,4-dioxane with powdered Zn in hexamethylphosphoramide (HMPA) was used for the synthesis of 1,4-dioxene 10 <1998JPP10067773>. To obtain substituted 1,4-oxathianes, the hydrogenation of the corresponding partially saturated compounds has been employed <2001J(P1)2604>. 

In dimethyl sulfoxide (80% )-tert-butyl alcohol solution at 27° 3°C. h At complete reaction, moles oxygen absorbed per mole substrate. c In hexamethylphosphoramide solution. d tert-Butyl alcohol solution. 

The Reformatsky reactions of ethyl a-bromopropionate and related esters with N-substituted 6-bromo-2-oxochromene-3-carboxamides in a mixed diethyl ether-benzene-HMPA-THF solvent system give substituted 9-bromo-2,3,4,4a,5,10b-hexahydro-l//-chromeno[3,4-f]pyridine-2,4,5-triones (HMPA = hexamethylphosphoramide Scheme 45) <2004RJ0892>. Without the THF present in the mixed-solvent system, the reaction stops at the intermediate Wbenzyl-6-bromo-4-(l-alkoxycarbonylalkyl)-2-oxochroman-3-carboxamide stage. 

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