Presence Of Hexamethylphosphoric Triamide Research Articles

Synthesis of hydrosilanes via Lewis-base-catalysed reduction of alkoxy silanes with NaBH4.

Hydrosilanes were synthesized by reduction of alkoxy silanes with BH3 in the presence of hexamethylphosphoric triamide (HMPA) as a Lewis-base catalyst. The reaction was also achieved using an inexpensive and easily handled hydride source NaBH4, which reacted with EtBr as a sacrificial reagent to form BH3in situ.

Synthesis and characterization of trinuclear and mononuclear rare-earth metal aryloxides supported by Salpn ligand and their application for the polymerization of rac-lactide

Four rare-earth metal complexes supported by Salpn ligand were synthesized, and their catalytic behaviors for the polymerization of rac-lactide (rac-LA) were explored. The amine elimination reactions of Salpn ligand LH2 (LH2=(CH2)3[N=CH(C6H4-2-OH)]2) with RE[N(SiMe3)2]3 (RE=Y, Yb, Sm, Nd) in a 1:1M ratio, and then with 1 equiv. of phenol ArOH (ArO=2,6-But2-4-MeC6H2O) in THF gave the trinuclear rare-earth metal aryloxo complexes [LRE(OAr)(HMPA)]3 (RE=Y (1), Yb (2), Sm (3)), and the mononuclear neodymium complex LNd(OAr)(HMPA)2 (4), respectively, in good yields in the presence of HMPA (HMPA=hexamethylphosphoric triamide). Complexes 1 and 2 can also be prepared by the phenol elimination reactions of (ArO)3RE(THF) with LH2 in a 1:1M ratio or salt metathesis reaction of LLi2(THF)x with anhydrous RECl3, then with NaOAr in THF. Complexes 1–4 were well characterized by elemental analyses and IR, as well as NMR spectroscopy in the case of complex 1. The definitive molecular structures of complexes 1–4 were determined by single-crystal X-ray analysis. The catalytic behaviors of these complexes for rac-LA polymerization were investigated. It was found that complexes 1–4 can initiate efficiently this polymerization and gave hetero-rich PLA. Kinetics study demonstrated that rac-LA polymerization initiated by complexes 1–3 has a first order relationship between polymerization rate and monomer concentration. A comparative kinetics study in THF and CHCl3 revealed that polymerization media have significant influence on the activity order of complexes 1–3 for rac-LA polymerization. The observed activity-increasing order of these complexes in THF is in agreement with the increasing order of their ionic radii, whereas it is in reverse order in CHCl3. A mechanism study demonstrated that the polymerization proceeded via a coordination-insertion mechanism, and the aryloxo group in these complexes acted as the initiating group.

ChemInform Abstract: Room-Temperature Metallation of 2-Substituted 1,3-Dithiane Derivatives and Subsequent Coupling with 2,3-Disubstituted Oxiranes.

2-Substituted 1,3-dithiane derivatives, (S)-1-(t-butyldiphenylsiloxy)-2-(1,3-dithian-2-yl)propane (9), (S)-1-(t-butyldimethylsiloxy)-2-(1,3-dithian-2-yl)propane, 1-(t-butyldiphenylsiloxy)-2-(1,3-dithian-2-yl)-2-methylpropane, and 1,2-bis(t-butyldiphenylsiloxy)-3-(1,3-dithian-2-yl)propane, were subjected to lithiation in THF with n-BuLi at room temperature (r.t.); the resulting anions reacted with 2,3-disubstituted oxirane, trans-2-methyl-3-(triphenylmethoxymethyl)oxirane (22), at r.t., giving the coupling products in satisfactory yield. On the other hand, the lithium salt formed in ether from (S)-2-(1,3-dithian-2-yl)-1-(4-methoxybenzyloxy)propane with n-BuLi at r.t. reacted with 22 at r.t. in the presence of hexamethylphosphoric triamide to afford the coupling product in moderate yield. In addition, a mixed organometallic reagent, n-BuLi / Bu2Mg, was found to be an effective metallation reagent for 9 and the resulting anion reacted with 22 to afford the coupling product in good yield.

Influence of hexamethylphosphoric triamide and dimethylformamide admixtures on the mechanism of tris(acetylacetonato)iron(III)-catalyzed ethylbenzene oxidation with molecular oxygen

The influence of electron-donating monodentate ligands L2, such as hexamethylphosphoric triamide (HMPA) and dimethylformamide (DMF), on the mechanism of tris(acetylacetonato)iron(III)-catalyzed oxidation of ethylbenzene with molecular oxygen was kinetically studied. It was found that the admixtures of L2 cause a nonadditive (synergistic) increase in the rate of ethylbenzene oxidation catalyzed by Fe(III)(acac)3, as well as a growth in the α-phenylethyl hydroperoxide selectivity (SPEH) and/or ethylbenzene conversion (C) relative to the Fe(III)(acac)3 catalysis in the absence of L2, changes that are due to the formation of more active complexes, mFe(III)(acac)3 · nL2 and Fe(II)(acac)2 · L2 (L2 is HMPA or DMF) and products of Fe(II)(acac)2 · L2 (L2 is DMF) transformation. The most significant effects of ligands L2 on SPEH and C was revealed in the case of catalysis by the {Fe(III)(acac)3-HMPA} system at 80°C. In the presence of the {Fe(III)(acac)3-DMF} catalyst system, methyl phenyl carbinol (MPC) was produced at a selectivity of SMPC ≅ 58%, a value that exceeds SPEH = 25–30% at the initial steps of ethylbenzene oxidation. The formation mechanism for the principal products—ethylbenzene hyroperoxide, acetophenone, and methyl phenyl carbinol—of ethylbenzene oxidation catalyzed by Fe(III)(acac)3 in the presence of HMPA and DMF was established. The activity of the Fe(II)(acac)2 · L2 complexes formed during ethylbenzene oxidation catalyzed by {Fe(III)(acac)3-L2} (L2 is HMPA or DMF) at the microsteps of chain initiation (O2 activation) and propagation in the presence of the catalyst (Ct) (Ct + RO2· →) was evaluated, and the role of these steps in the mechanism of the iron-catalyzed oxidation of ethylbenzene to α-phenylethyl hydroperoxide was discussed.

Synthesis and Characterization of the First Dinuclear Europium (II) Complex Supported by Carbon-Bridged Biphenolate Ligand

Anhydrous EuCl 3 reacted with sodium carbon-bridged biphenolate LNa 2[L = 2,2′-methylene bis(6-tert-butyl-4-methyl-phenoxo] in a 1:1 molar ratio in THF in the presence of HMPA (HMPA = hexamethylphosphoric triamide), then the product formed in situ was reduced by Na-K alloy to generate the divalent carbon-bridged biphenolate europium complex [LEu(HMPA) 2] 2(THF) 4(1) in a good isolated yield. Complex 1 was fully characterized by elemental analysis, NMR and IR spectra, and X-ray structural determination. The crystal data of complex 1 are monoclinic, P2 1/ c space group, a = 1.6521(3) nm, b = 2.8274(3) nm, c = 1.2074(2) nm, β = 111.723(6)°, V = 5.2393(14) nm 3, Z = 2, D c = 1.259 mg·m −3, μ = 1.304 mm −1, F(000) = 2092, R = 0.0815, wR = 0.1723. Complex 1 is a dimer with two Eu - 0 bridges. The coordination geometry of each europium atom can be best described as a distorted trigonal bipyramid.

Cyclopropanation of N‐Substituted 2‐Oxochromene‐ and 6‐Bromo‐2‐oxochromene‐3‐carboxamides with Zinc Enolates Derived from 1‐Aryl‐2,2‐dibromoalkanones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cyclopropanation of N-Substituted 2-Oxochromene- and 6-Bromo-2-oxochromene-3-carboxamides with Zinc Enolates Derived from 1-Aryl-2,2-dibromoalkanones

Zinc enolates derived from 1-aryl-2,2-dibromoalkanones react with N-cyclohexyl-2-oxochromene-3-carboxamides to give N-cyclohexyl-1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides mainly as cis isomers with respect to the substituents in positions 1 and 1a. Reactions of the same zinc enolates with N-benzyl-2-oxochromene-3-carboxamide and N-benzyl-6-bromo-2-oxochromene-3-carboxamide lead to formation of 1-aryl-2-benzyl- and 1-aryl-2-benzyl-6-bromo-1-hydroxy-9c-alkyl-1,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[1,2-a]naphthalene-3,4-diones. The reaction of zinc enolates with N-aryl-2-oxochromene-3-carboxamides in a weakly polar solvent (diethyl ether or ethyl acetate) affords mixtures of cis-N-aryl-1-aroyl-1-alkyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides and their cyclic isomers, 9c-alkyl-1,2-diaryl-1-hydroxy-1,2,9b,9c-tetrahydro-5-oxa-2-azacyclopenta[2,3]cyclopropa[1,2-a]naphthalene-3,4-diones, the latter prevailing. N-Substituted 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxamides in which the aroyl group on C1 and the carboxamide group on C1a are arranged trans are formed by reactions of zinc enolates with the corresponding 2-oxochromene-3-carboxamides in the presence of hexamethylphosphoric triamide.

(-)-(R)- and (+)-(S)-Carvone in the Synthesis of Optically Active Acetylenic Alcohols, Ethers, and Dichlorosilyl Derivatives

Reaction of butyllithium with acetylene and 1-hexyne gave the corresponding lithium acetylides which reacted with (-)-(R)- and (+)-(S-carvone in a stereospecific fashion to give lithium (1-ethynyl- or 1-hexynyl)-5-isopropenyl-2-methyl-2-cyclohexenolates. Hydrolysis of the latter gave individual optically active tertiary terpene alcohols having both acetylenic and p-menthene fragment. Their treatment with methyl iodide in the presence of hexamethylphosphoric triamide afforded the corresponding methyl ethers. The reaction of 3-ethynyl-5-isopropenyl-3-methoxy-2-methylcyclohexene with butyllithium and trichloro(vinyl)silane yielded optically active dichlorosilyl-containing acetylenic compounds.

Degenerate Transesterification of Dimeric Lithium 2,4,6-Trimethylphenolate and a Further Observation on the Reaction of Tetramers1

The rates of exchange of the 2,4,6-trimethylphenolate ion between dimeric lithium 2,4,6-trimethylphenolate-d9 and a series of 2,4,6-trimethylphenyl esters [2,4,6-(CH3)3C6H2COOCH2R; R = CH2CH3, CH3O, Ph, 4-CH3Ph, 4-CF3Ph, 4-ClPh, 4-CH3OPh, 2-pyridyl, and 4-pyridyl] have been determined in dioxolane, THF, 1,2-dimethoxyethane, and pyridine. The reactions are first order in the lithium phenolate showing that the dimer reacts without dissociation. The rates of transesterification increase with increasing solvent donicity in contrast to the reaction of tetrameric lithium 3,5-dimethylphenolate. For all the esters, except R = 2-pyridyl, the rates of transesterification exhibit a linear correlation with their rates of hydrolysis. The 2-pyridyl ester exhibits an abnormally high rate of transesterification, which is attributed to a complex-induced proximity effect. Tetrameric lithium 3,5-dimethylphenolate undergoes transesterification less rapidly in the presence of hexamethylphosphoric triamide (0.25−1.6 equiv), a ...

Synthetic, structural, spectroscopic and calculational studies of a lithium β-diketinimate complex

Reaction of malonaldehyde bis(phenylimine) monohydrochloride with two equivalents of n-BuLi in the presence of hexamethylphosphoric triamide (HMPA) yielded crystals of [PhN(CH) 3NPhLi·HMPA] 2. The two LiN 2C 3 metallacycles of the dimeric molecule are linked by two bridging oxygens from HMPA. No spectroscopic evidence for dissociative or other equilibria was obtained. The lithium projects above the mean plane of the metallacycles. MNDO calculations on model compounds reproduced bond lengths and angles well, except that all minima were planar, ascribing the envelope conformation to a packing effect. The molecule could best be described as a 1,5-diphenyl-1,5-diazapentadienyl lithium complex, the anion having contributions from diketinimato and two equivalent keteneimine-ene-amido resonance forms. In contrast, the protonated ligand exists in a localized keteneimine-ene-amine form only.

SmI 2-Mediated coupling reactions between iodoalkynes and ketones or aldehydes to give propargyl alcohols

Samarium iodide (SmI 2) mediates a coupling reaction between alkynyl iodides and ketones or aldehydes to give propargyl alcohols in the presence of hexamethylphosphoric triamide (HMPA) in either benzene or tetrahydrofuran (THF). An alkynylsamarium is involved as an intermediate.

Highly effective diastereodifferentiation of Meso-dicarboxylic anhydrides using sterically congested chiral N-sulfonylaminoalcohols

The differentiation between enantiotopic carbonyl groups of cyclic meso-dicarboxylic anhydrides has been attained with excellent diastereofacial selectivity with an isomer ratio above 99 : 1 by treatment with the lithium salts of sterically hindered chiral N-arylsulfonyl-2-aminoalcohols in the presence of hexamethylphosphoric triamide.

Synthesis and reactions of uranium(IV) tetrathiolate complexes

Uranium(IV) tetrathiolate complexes were made by (a) reaction of U(NEt2)4 with RSH (R = Et, Pri, Bun or But), (b) treatment of U(BH4)4 with RSH (R = Bun or Ph) or of U(SBun)4 with PhSH or (c) oxidation of uranium metal by RSSR (R = Et, Pri or Ph). Rearrangement of [U(SBut)4(py)3](py = pyridine) in toluene gave the trinuclear cluster [U3S(SBut)10] with liberation of ButSH and Me2CCH2. Reaction of U(SPri)4 with [NEt3H][BPh4] in the presence of hexamethylphosphoric triamide (hmpa) afforded the cationic compound [U(SPri)2(hmpa)4][BPh4]2 which presents a trans-octahedral crystal structure. Iodinolysis of U(SPri)4 in pyridine led to the formation of [U(SPri)2l2(py)3] which adopts a pentagonal-bipyramidal configuration in its crystalline form. The trithiocarbonate (PriS)2CS was obtained by reaction of U(SPri)4 with CS2.

Reductive elimination of glycosyl phenyl sulfones by SmI 2-HMPA: A convenient synthesis of substituted pyranoid glycals

A series of substituted glycosyl phenyl sulfones was converted into glycals after reductive samariation with SmI 2 in the presence of hexamethylphosphoric triamide, followed by elimination of the substituent at C-2. Practically quantitative yields were obtained when the leaving group was an acetate, as illustrated here with seven substrates.

New entries to fluoropyridine and fluoroquinoline heterocycles

Fluoropyridines and fluoroquinolines can undergo selective hydrogen/metal exchange and subsequent electrophilic substitution. The yields are better when the superbasic mixture of lithium diisopropylamide and potassium t-butoxide (LIDA-KOR) [C. Margot and M. Schlosser, Tetrahedron Lett., 26 (1985) 1035; A. Mordini, E. Ben Rayana, C. Margot and M. Schlosser, Tetrahedron, 46 (1990) 2401] rather than lithium diisopropylamide in the presence of hexamethylphosphoric triamide [F. Marsais, E. Bouley and G. Quéguiner, J. Organometall. Chem., 171 (1979) 273] is employed as the metalation agent. ▪ The required fluoroheterocyclic precursors can be prepared by the Schiemann-Balz reaction. A novel, very efficient method consists of acid catalyzed cyclization of suitably substituted α-fluoroacrylanilides, e.g.: ▪ α-Fluoroacrylic acid and derivatives thereof are readily accessible by solvolytic ring opening of gem-dialkoxy- or gem-alkoxy(trimethylsilyloxy)- 1-chloro-1-fluorocyclopropanes [Method: Y. Bessière and M. Schlosser, Helv. Chim. Acta, 60 (1977) 590]. Alternatively, they can be obtained by the Wittig reaction using α-alkoxycarbonyl or α-carbamoyl-substituted (triphenylphosphonic) fluoromethamides. ▪

Reductive desulfonylation of phenyl sulfones by samarium(II) iodide-hexamethylphosphoric triamide

Samarium(II) iodide in tetrahydrofuran reductively desulfonylates phenyl sulfones in the presence of hexamethylphosphoric triamide. This transformation is illustrated here for ten substrates, which include secondary alicyclic, β-hydroxy, vicinal bis-, and α,β-unsaturated sulfones.

Silylene complexes stabilized by sulphur substituents; a structure and reactivity study

A new base-stabilized silylene (silanediyl) complex (t-BuS) 2(HMPA)SiFe(CO) 4 ( 9b) has been prepared from Na 2Fe(CO) 4 and (t-BuS) 2SiCl 2 ( 2b) in the presence of HMPA (hexamethylphosphoric triamide). An X-ray structure analysis of 9b shows the silylene coordinated to the iron atom [Fe—Si = 2.278(1) Å]. The HMPA is bound via its oxygen atom to the unsaturated silicon [O—Si 1.734(2) Å], which adopts a distorted tetrahedral coordination geometry. A comparison of 9b with the analogous oxo compound (t-BuO) 2(HMPA)Si Fe(CO) 4 ( 9a) indicates an almost identical stabilizing effect of the electron-deficient silicon atom in 9b by π-mesomeric and polarization effects of the t-BuS substituents. The conformation of the substituents found at the silicon atom is reproduced by a force field calculation. A base-free silylene complex (t-BuS) 2SiFe(CO) 4 (10) has been observed directly by NMR spectroscopy ( 1H NMR: δ 1.70, s; 29Si NMR: δ 83.2, s) and was further characterized by a derivatization reaction with HMPA to form 9b. The HMPA adduct 9b is a valuable model compound for mechanistic investigations: photolysis of 9b in the presence of 2,3-dimethylbutadiene as trapping reagent yields 1,4-addition of the silylene to the butadiene. In the absence of any trapping reagents, polysilanes are formed. The experiments provide evidence for a silylene cleavage mechanism.

Trimethylsilylation of Propargyl Chloride and Propargyl Bromide

Abstract Me3SiC[tbnd]CCH2Cl and Me3SiC[tbnd]CCH2Br are obtained in high yields by treating propargyl chloride and bromide, respectively, with n-butyllithium and lithium diisopropylamide and subsequently adding chlorotrimethylsilane in the presence of hexamethylphosphoric triamide (HMPT). An effective method for the purification of HMPT is described.

The Hydroboration of 1-Alkylthio-l-alkynes, and Its Application to the Syntheses of S-Alkyl Alkanethioates and (Z)-1-Alkylthio-1-alkenes

Abstract Hydroboration of 1-alkylthio-1-alkynes with dicyclohexylborane or bis(1,2-dimethylpropyl)borane proceeded smoothly, adding most of the dialkylboryl group to the α-position of the triple bond. The resulting alkenylboranes afforded either S-alkyl alkanethioates on a controlled oxidation with alkaline hydrogen peroxide in the presence of N,N,N′,N′-etramethylethylenediamine or (Z)-1-alkylthio-1-alkenes on a basic protonolysis, successive treatments with methyllithium, copper(I) iodide and water in the presence of hexamethylphosphoric triamide.

Stereoselective Synthesis of α,β-Epoxy Ketones by the Darzen's Reaction with MethylN-Ethyl-N-tributylstannylcarbamate

Methyl N-ethyl-N-tributylstannylcarbamate is shown to be an efficient reagent for the Darzen's reaction. Its reactivity is increased by the addition of equimolar amounts of hexa-methylphosphoric triamide. The stereoselectivity of the product is controlled by the conditions, such as the halogen group of the substrate and the presence of hexamethylphosphoric triamide. This method is the first example of the stereoselective synthesis of cis-epoxy ketones by a one-pot Darzen's reaction of α-halo ketones and aldehydes.