Hexamethylphosphorus triamide

The lrialkyl(trifluorovmyl)slannanes were used in the Pd(0)-catalyzed coupling reaction of aryl halides [77] (equation 12). The product yield increased with the solvent type in the order hexamethylphosphorus triamide (HMPT) DMF > dimethyl sulfoxide (DMSO) > tetrahydrofuran (THF) > CgHg > C2H4CI2. 

Heterocycle 108 was obtained in 45% yield by the reaction of dilithiated A-ethynylpyrrole 110 with elemental tellurium followed by a treatment of the reaction mixture with hexamethylphosphorus triamide [95JOM(493)271]. 

The hexamethylphosphorus triamide is obtained from the Eastman Kodak Company. It is distilled under reduced pressure (water aspirator) to yield a clear, colorless oil, b.p. 46-48° (7 mm.). It is then stored under nitrogen (rubber septums should be avoided as they tend to deteriorate on prolonged contact with phosphine vapors). Hexamethylphosphorus triamide that has not been freshly distilled often requires much longer reaction times. Since this chemical is an irritant, all operations with it should be performed in a well-ventilated hood. Hexamethylphosphoramide is a classified carcinogen see Org. Syn., 55, 103 (1976). It should not be confused with hexamethylphosphorus triamide used in this preparation. 

A 20% excess of hexamethylphosphorus triamide is utilized to increase the reaction rate. When a 10% excess of the phosphine is used, the reaction is not quite complete (as monitored by gas chromatography) even after 3 hours. If the reaction is not allowed to go to completion, the chromatographed product will contain benzyl disulfide. Note that the desulfurization rate for hexaethyl-phosphorus triamide is comparable to that for hexamethylphosphorus triamide. However, the chromatographic separation following the reaction is much more efficient when hexamethylphosphorus triamide is used. 

Aromatic aldehydes can be dimerized to epoxides by treatment with hexamethylphosphorus triamide.698 The reagent699 is converted to hexamethylphosphoric triamide (HMPA), The reaction can be used for the preparation of mixed epoxides by the use of a mixture of two aldehydes in which the less reactive aldehyde predominates. Epoxides have also been pre-... 

The reaction of m-3,5-di(isopropoxycarbonyl)-l,2-dithiolane 113 in dichloromethane with hexamethylphosphorus triamide (HMPT), added over a period of 12 h at room temperature, led to the formation of tram-2,4-di(isopropoxy-carbonyllthietanc 114 in 27% yield (Equation 33) <2000J(P1)1595>. 

Dehydration of 124 to the expected 1-seleno-l-vinylcyclopropanes was succesful only with tertiary alcohols of this type it required the use of thionyl chloride in the presence of triethylamine, pyridine or hexamethylphosphorus triamide followed by reaction with potassium t-butoxide in DMSO, or the use of the Burgess reagent... 

Methylcopper is less reactive than lithium dimethylcopper towards acid halides (295), but the yield of methyl ketones can be increased by performing the reaction in hexamethylphosphorus triamide (HMPT) or CHgCN (224). 

Alternative methods for preparing solvated alkali-metal graphites include either secondary solvation of the binary compounds or reduction of graphite by solutions of the alkali metal in electron-solvating media such as hexamethylphosphorus triamide (HMPT) or polycyclic aromatic systems in ethers , leading, e.g., to HMPT- or ether-solvated compounds. 

CARBONATES N,N -Carbonyldiimidazole. Hexamethylphosphorus triamide-Dialkyl azodicarboxylates. 

ETHERS Antimony(V) fluoride. Hexamethylphosphorus triamide. Tetra-n-butyl hydrogen sulfate. Thallium(I) ethoxide. Triphenylphosphine-Diethyl azodicarboxylate. ETHYL KETONES Sodium tetracarbonylferratefll). 

Mitscher and co-workers (30) have explored alternative methods of synthesizing 3-prenyl-2-quinolones (Scheme 2) whereby the formation of by-products characteristic of the prenylmalonate route is avoided by blocking the 3-position. Thus, allylation of the 3-bromo-4-hydroxy-Af-methyl-2-quinolone yielded ketone 19 which, with zinc and acid, was converted into the 3-prenyl-2-quinolone (20). The ketone 22, obtained from ester 21, was transformed into the 2-quinolone (20) by heating with copper acetate in hexamethylphosphorus triamide. 

Only moderate variations in kinetic ElZ) ratios are observed except for LHDS, which favored the thermodynamically more stable (Z) enolate. The sterically demanding LTMP favored formation of the kinetic E enolate.22 An equilibration process is clearly occurring, possibly by an aldol addition — retro-aldol process that was suggested by Rathke and co-workers (via 26). The aldol condensation will be discussed in Section 9.4.A. Addition of HMPT (hexamethylphosphorus triamide) destabilizes and deaggregates aldolate 26, promoting equilibration. 

In the conversion of 66 to 67, we saw that HMPA was used as an additive. Another useful ingredient in many alkylation reactions is hexamethylphosphorus triamide [HMPT, (Me2N)3P], which coordinates with the enolate anion, diminishing the aggregate state and increasing reactivity. This additive also enhances the polarity of the solvent and thereby enhances the facility of the Sn2 alkylation step (sec. 2.7.A.i). The use of an additive such as HMPA or HMPT is very common when the enolate anion reacts slowly and/or the halide is relatively unreactive. Other acid derivatives such as lactones can react with LDA to give an enolate anion, which then reacts with alkyl halides in the usual manner. 

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