Addition Of Hexamethylphosphoric Triamide Research Articles

An efficient method for converting alcohols to azides with 2,4,4,6-tetrabromo-2,5-cyclohexadienone/PPh 3/Zn(N 3) 2·2Py

Treatment of the salt generated from 2,4,4,6-tetrabromo-2,5-cyclohexadienone and PPh 3 in a mixed solvent of CH 3 CN toluene with primary and secondary alcohols in the presence of Zn(N 3) 2·2Py led to azides in excellent yields with inversion of configuration. Addition of hexamethylphosphorictriamide considerably accelerated the reaction.

Study on the reduction species of sulfur by alkali metals in nonaqueous solvents

Rechargeable cells with a sulfur cathode, a lithium anode and a nonaqueous electrolyte operating at ambient temperature have been extensively studied as a possible application of sulfur combined with nonaqueous solvent. However, the behavior of the chemical species formed by the reduction of sulfur with alkali metals in nonaqueous solvent has not yet been clarified. In this report, sulfur is reduced in tetrahydrofuran (THF) by alkali metals (M: Na, K, Li and Cs), by anthracene radical anions or by diphenylethylene dimer dianions with alkali metal counter cations mainly under the experimental condition of [S 8] [M] > 0.25 . The system produced by the reduction is the yellow solution consisting of polysulfide dianions ( S m 2−, m > 1) and radical anions ( S n −, n > 1) which changes into a blue solution by the addition of hexamethylphosphoric triamide with a much higher polarity than THF. The influence of the kind of alkali metal, the temperature and the addition of solvents such as crown ether on the behavior of the chemical species formed are examined by ultraviolet ( uv)-visual electronic spectra, electron spin resonance (ESR) spectra and Raman spectra measurements. In addition, γ-irradiation with 60Co was carried out to reduce sulfur in glassy solid 2-methyl-THF at — 196 °C. Furthermore, the reaction between the yellow solution and aliphatic bromide is investigated. As a result, it is revealed that the yellow species is S 4 2−, the blue species is S 3 − and several polysulfide dianions and radial anions are in a state of equilibrium.

Structural studies of lithiated enaminones: the 1-oxa-5-azapentadienyllithium fluxional heterocubane [(PriNCMeCHCMeOLi)4] and its dimeric hexamethylphosphoric triamide complex [{PriNCMeCHCMeOLi·OP(NMe2)3}2

Lithiation of 4-isopropylaminopent-3-en-2-one in hexane gave a 1-oxa-5-azapentadienyl compound [(PriNCMeCHCMeOLi)4] 1, which comprises a tetrameric aggregate of Li4 and O4 interpenetrating tetrahedra in which chelating terminal nitrogens undergo a fluxional process around each face of the Li4 tetrahedron in toluene solution. Addition of hexamethylphosphoric triamide (hmpa) produced a dimeric complex 2 in which oxygen bridges are retained. The crystal structures of both compounds were determined. Bond lengths indicate that an iminoenolate form of the ligand predominates, irrespective of aggregation state. The data are used to rationalise the selectivity of dimetallations of enaminones.

REACTION OF POLYMERIZATION-RESISTANT 1,2-DITHIOLANES WITH LITHIATED PICOLINES: SIMPLE RING OPENING AND 1,3-DITHIANE FORMATION

Abstract Reaction of polymerization resistant 1,2-dithiolanes 1 with excess pyridylmethyllithiums 3 in THF gave the corresponding ring-opened products 2 in good yields, but the by-products 2-pyridyl-1,3-dithianes 5 and 1,3-propanedithiols 6 could not be excluded. Addition of hexamethylphosphoric triamide (HMPT) to the reaction mixture resulted in the selective formation of 5.

Nitrosation of ketone dianions.

Nitrosation of α, α'-dianions produced from ketones using a couple of bases was carried out with tert-butyl nitrite(tert-BuONO) in ether, and then two regioisomers of oximes(but not acetone)were obtained simultaneously. The ratio of these regioisomers was remarkably reversed by the addition of hexamethylphosphoric triamide(HMPA).

Hydrometallurgical methods for extraction and purification of silica

Two methods using nonaqueous solvents for extraction and purification of silica were studied. The “nonaqueous solvent re-leaching method” was studied as part of a three stage process. Stage 1: Ore containing acid soluble silica was leached with low boiling point acid. Stage 2: Leach liquor was heated to vaporize the residual acid and a cake is obtained. Stage 3: The cake was then leached with nonaqueous solvent (i.e. re-leaching) and filtered. This method has been applied to the treatment of manganese nodules and garnierite, and silica-free or low silica-containing leach liquor could be obtained. Also, another three stage process “nonaqueous solvent precipitation method” was studied. Stage 1: Ore containing alkali soluble silica was leached with alkali and filtered. Stage 2: Leach liquor was added into a nonaqueous solvent such as methanol or ethanol and the silica sediment obtained. Stage 3: The silica sediment was washed with acid. This method has been applied to the treatment of diatomaceous earth and garnierite. By this method, impurities other than Al and Ti could be removed effectively, but Al and Ti had tendencies to remain in the silica. But, pretreatment of the alkali leach liquor by oxine, and/or addition of hexamethyl phosphoric triamide during leaching could lower Al and Ti.

New Methods and Reagents in Organic Synthesis 89. Studies on Reaction Conditions and New Entry to Chiral Ligands in the Chiral Lithium Amide-Mediated Enantioselective Aldol Reaction.

Reaction conditions for the enantioselective aldol reaction of 2, 2-dimethyl-3-pentanone (3) and benzaldehyde using the chiral lithium amide 1b as a chiral auxiliary were thoroughly investigated. All three procedures, that is, (1) the combined use of lithium diisopropylamide and the chiral lithium amide 1b, (2) the use of an excess of the chiral lithium amide 1b, and (3) the regeneration of the chiral lithium amide 1b, afforded the aldol 4 in about 90% yield and 70% enantiomeric excess (ee). Investigation of the effects of solvent by utilizing 1-naphthaldehyde revealed that in tetrahydrofuran, (S, S)-aldol 5 of 77% ee was obtained as the major product, while in ether (R, R)-5 became the major isomer (38% ee). Furthermore, addition of hexamethylphosphoric triamide caused a dramatic change of stereoselectivity, and (S, S)-5 of 70% ee was obtained in ether with 20 eq of hexamethylphosphoric triamid. The aldol 4 of 74% ee was obtained when the new chiral lithium amide 6b was used.

SmI 2-induced reductive cross-coupling of carbonyl compounds with (α,β-unsaturated esters

Reductive cross-coupling of carbonyl compounds with(α,β-unsaturated esters by SmI 2 to ?-lactones was highly accelerated by the addition of hexamethylphosphoric triamide (HMPA).

Chemistry of 2H‐thiopyran and derivatives IV. Deprotonation and methylation of 2H‐thieno[2,3‐b]thiopyran and some derivatives

AbstractMetallation of 2H‐thieno[2,3‐b]thiopyran 1 by strong bases under relatively apolar conditions proceeds exclusively in the 2‐position of the thiophene ring. In polar media a 2‐proton of the thiopyran ring is removed to give the anion 1b. By addition of hexamethylphosphoric triamide (HMPT) to the lithiated compound 1a conversion into 1b takes place. The anions 1a and 1b react with methyl iodide to give the compounds 2 and 3, respectively. Compound 2 can be further methylated by reaction with BuLi in tetrahydrofuran (THF)/HMPT mixtures or sodamide in liquid NH3, followed by addition of methyl iodide. The resulting compound 4 can be converted into the compounds 5, 6 or 7, depending on the base‐solvent system: Compound 5 is produced by interaction between 4 and KNH2 in liquid NH3 at − 33°, followed by methylation at − 60°. If the reaction with KNH2 is carried out at − 60°, however, methylation gives 6, this result is also obtained from 4, BuLi in THF/HMPT and CH3I. Omission of HMPT during the metallation gives rise to vinylic proton abstraction, and subsequent addition of CH3I leads to 7.

Mechanism of electrophilic substitution with participation of ion pairs in organometallic chemistry ( SE2 ion pair mechanism)

A new mechanism S E2 ion pair) has been suggested for the reaction of organotin compounds with electron-withdrawing groups (R = 9-Me-fluorenyl, indenyl, PhC C etc.). It has been shown that some RSnMe 3 compounds may undergo ionization or dissociation in polar solvents. In low-polar solvents optically active indenyl derivatives of tin racemize slowly but the rate of racemization is increased by addition of hexamethylphosphoric triamide. This result was explained by the loss of configuration when the ion pair R −Sn +Me 3 reverts to the covalent form.

Chemistry of 2H‐thiopyran and derivatives I. 2H‐ versus 6H‐proton abstraction from 2H‐thiopyran

AbstractDepending on the nature of the base/solvent system deprotonation at carbon atoms 2 and 6 in 2H‐thiopyran 1 can be carried out specifically. Conversion of 6‐lithio‐2H‐thiopyran (4) into the charge‐delocalised species 2 takes place in the presence of diisopropylamine, probably via a process of proton donation and abstraction. Addition of hexamethylphosphoric triamide (HMPT) to the solution of 4 also gives rise to the formation of the thermodynamically more stable species 2.

Chain extension reactions of acetylenes. Part 2. A comparison of the reactions of butyl-lithium with 1-iodoalk-1-ynes and 1-bromoalk-1-ynes

1-lodohept-1-yne reacts with 2 equiv. of butyl-lithium to form octane and hept-1-yne, whereas 1-bromohept-1-yne undergoes butylation at C-3. In the presence of 1 equiv. of butyl-lithium, metal–halogen exchange gives butyl iodide and lithium hept-1-ynide, which couple to form undec-5-yne on addition of hexamethylphosphoric triamide. The reaction of 2 equiv. of butyl-lithium with either 1-bromo- or 1-iodo-propyne gives largely octane, but chain extension of 1-bromopropyne occurs to give hept-1-yne when 3 equiv. of butyl-lithium are used and butyl bromide is then added. Addition of iodine after butyl bromide gives 1-iodohept-1-yne.