Hexamethylphosphoramide as solvent

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

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 Hexamethylphosphoramide as solvent 20, 30, 119, 477, 628 Hexokinase as reagent 18, 151 High dilution, technique s. a. 

The reduction of enones by electron transfer has been studied further, a comparison being drawn between ammonia and hexamethylphosphoramide as solvents. In general, reduction with sodium in hexamethylphosphoramide yields more of the less stable saturated ketone epimer than is observed in ammonia methods of optimizing this selectivity are discussed. ... 

If PTC is not used, then a polar aprotic solvent is essential to solubilize the ionic nucleophile well enough for efficient reaction to occur. Chen has used hexamethylphosphoramide as solvent for the esterification of poly(sodium acrylate) with bromoalkyl mesogens while Pugh and Percec used dimethyl formamide (DMF) for the etherification of sodium 4-methoxybiphenoxide with poly(epichlorohydrin). In a compromise between PTC and single-solvent approaches, Maa and Chen have reported the efficient esterification of acrylic polymers with bromoalkylmesogens in DMF after isolating the tetrabutylammonium salts of the polyac-rylates (tetrabutylammonium compounds are common PT catalysts). 

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). 

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... 

The solvent used was hexamethylphosphoramide. As in the production of formic acid (160), this reaction is markedly accelerated by the addition of water, and a proposed mechanism includes the formation of formic cid and its subsequent decomposition to CO and H20, with the CO being bound by the rhodium, (82). 

In attempts to prepare 3-acyl-substituted BIPS (113), various salicylaldehydes were condensed with l,3,3-trimethyl-2-formylmethyleneindoline (Fischer s aldehyde). In alcohol, dimethylformamide, tetrahydrofuran, Y-mcthylpyrrolidonc. and hexamethylphosphoramide as the sole solvents, decarbonylation occurred and the only products were the BIPS compounds. However, in dimethyl sulfoxide, 5-nitro-and 3-bromo-5-nitrosalicylaldehydes gave 11 and 5.6% of the desired 3-formyl-BIPS, respectively. The structures were assigned from their IR and NMR spectra. 

With pure hexamethylphosphoramide as the solvent for polystyryl sodium the dissociation equilibria lie far on the side of loose ion pairs and free carboanions. Individual rate constants for propagation have been determined and shown to be similar to those in ethereal solvents, though in this case is very much higher, -10 M. 

These stereochemical results obtained by Bachelor and Bansal, using r-butyl alcohol as solvent, differ from those observed in a study using hexamethylphosphoramide (HMPA). In a subsequent paper, it is suggested that the differences must be attributed to differences in the degree of reversibility of the aldol step in the two solvents when irreversible aldolization is ensured (by appropriate modification of reaction conditions), the stereochemical results obtained in HMPA, ether and r-butyl alcohol/ether are essentially the same. - In HMPA, it was found that this condition is reached at ambient temperature, however in r-butanol/ether the aldol step has a significant component of reversibility above -40 C. Similar observations have been reported by Villieras and Combret in a study of the condensation of isobuty-raldehyde with alkyl chloroacetates (equation 7). The results of this study are summarized in Table 2. The results at room temperature are similar to those shown in Table 1 the ratio of c -epoxide increases as the size of the ester substituent increases. However, at low temperature the corresponding ratios of... 

The parameters of the Mossbauer spectra recorded in pyridine-hexa-methylphosphoramide agreed, within the limits of experimental error, with the data for solutions containing only pyridine as solvent, even in systems containing a large excess of hexamethylphosphoramide (e.g., in a solution with an HMPA content of 90%, v/v). 

Startg. m. allowed to react at -78 under Ng with ec-butyllithium in anhydrous tetrahydrofuran containing 4% hexamethylphosphoramide as strongly coordinate ing solvent product. Y 86%. W. C. Still, Tetrah. Let. 7976, 2115. 

Critical reviews on ylides, enamines, and nitrenes have been published. Brown has reported on the reactivity and selectivity of diborane and disiamylborane with a range of functional groups. The properties of hexamethylphosphoramide as a solvent and a reagent have been catalogued ... 

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