Addition Of HMPA Research Articles

Aminolithiation–arylation consecutive cyclization of N-(2-fluorophenyl)methylaminoalkylstyryls giving aryl-substituted pyrido[1,2-b]isoquinolines

Aminolithiation–arylation tandem cyclization of N-(2-fluorophenyl)methylaminoalkylstyryls proceeded smoothly to give hexahydro-2H-pyrido[1,2-b]isoquinoline using a stoichiometric amount of n-BuLi with high trans selectivity. The arylation reaction was highly accelerated by the addition of HMPA. Both pyrido- and pyrrolo-[1,2-b]isoquinoline were successfully constructed by this tandem reaction.

ChemInform Abstract: Stereoselective Synthesis of Alcohols Containing (Z)- and (E)-Olefins, Dienes, Enynes and Styrenes: Cyclic β-Halogeno Ether Scissions Using Samarium Diiodide as the Electron-Transfer Agent.

In contrast to the sodium-mediated ring scission of 2-substituted 3-chloro ethers of the tetrahydrofuran series, samarium diiodide gives olefins of high (E)-stereoselectivity and provides (E)-conjugated and unconjugated dienes, styrenes and enynes in good yield without appreciable over-reduction. Whilst the SmI2 scission of 3-chloro-2-alkyltetrahydropyrans gives(Z)-rich (Z)/(E) olefin mixtures, the 2-(alk-1′-ynyl) members give (Z)-enyne alcohols with high stereoselectivity, providing a valuable complement to the (E)-enyne synthesis employing the tetrahydrofuran series.In electron-transfer scissions using sodium, the stereochemistry of the product alcohols is related to the ground-state conformation of the cis- and trans-pyrans and -furans. The slow SmI2-mediated reactions appear to involve samarium-complexed intermediates aving structures independent of the original conformation, or of the cis- or trans-geometry of the furan or pyran, and it is the transition states from these intermediates that determine the stereochemical outcome.Scissions in the tetrahydrofuran series can be accelerated by addition of HMPA or DMPU with only a little deterioration in stereoselectivity, but in the tetrahydropyran series there are drastic changes in product stereochemistry when DMPU is added. Brief comment is made on the synthesis of tetrahydro-furan and -pyran precursors.

Stereoselective alkylations of chiral nitro imine and nitro hydrazone dianions. Synthesis of enantiomerically enriched 3-substituted 1-nitrocyclohexenes.

Dianions of chiral nitro imines (generated by a combination of LDA and s-BuLi) underwent diastereoselective alkylation with methyl, butyl, isopropyl, allyl, and methallyl iodides. In contrast to the behavior of simple metalloenamines, the most selective auxiliary contained no coordinating groups but did possess a large steric difference between the two substituents. The yield and selectivity of the alkylations were improved by the addition of HMPA or DMPU. The use of (S)-1-naphthylethylamine as the auxiliary afforded the R absolute configuration of the alkylation products. This stereochemical outcome could be rationalized by simple steric approach controlled alkylation in a conformationally fixed, internally coordinated dianion. A SAMP nitro hydrazone gave poorer yields and selectivities.

Reactivity of the Triple Ion and Separated Ion Pair of Tris(trimethylsilyl)methyllithium with Aldehydes: A RINMR Study

Low-temperature rapid-injection NMR (RINMR) experiments were performed on tris(trimethylsilyl)methyllithium. In THF/Me2O solutions, the separated ion (1S) reacted faster than can be measured at -130 degrees C with MeI and substituted benzaldehydes (k >/= 2 s -1), whereas the contact ion (1C) dissociated to 1S before reacting. Unexpectedly, the triple ion reacted faster with electron-rich benzaldehydes relative to electron-deficient ones. The addition of HMPA had no effect on the rate of reaction of the triple ion with p-diethylaminobenzaldehyde, and the immediate product of the reaction was the HMPA-solvated separated ion 1S, with the Peterson product forming only slowly. Thus, the aldehyde is catalyzing the dissociation of the triple ion. HMPA greatly decelerated the reaction of 1S (<10 -10), providing an estimate of the Lewis acid activating effect of a THF-solvated lithium cation in an organolithium addition to an aldehyde.

Preparation of novel bicyclic piperazines by reduction of bicyclo[4.2.2]diketopiperazines: rearrangement involving 1,2-bond migration

Reduction of (1 R,6 R)-7,9-diazabicyclo[4.2.2]dec-3-ene-8,10-dione ( 5) with lithium aluminum hydride gave a mixture of the expected (1 R,6 R)-7,9-diazabicyclo[4.2.2]dec-3-ene ( 2) as well as 7,9-diazabicyclo[4.3.1]dec-3-ene ( 3), resulting from 1,2-σ (C–C) migration of the pendant cis-2-butenyl ring. More of the rearranged product was observed in polar solvents and upon the addition of HMPA. The relief of ring strain imparted by the olefin may promote this rearrangement, as it was not observed when the olefin was reduced prior to the reduction.

Effect of Additives on Hydrolysis of Ti Alkoxide and Microstructural Observation of TiO&lt;sub&gt;2&lt;/sub&gt;

By the usage of the hydrolysis of Ti alkoxide, various types of TiO2 were obtained through the addition of catalyst (HCl, NH4OH, and CH3COONH4) and some additives into Ti alkoxide solution at room temperature. In special, the effect of two additives, diethylene glycol (DEG) and hexamethylphospheric triamide (HMPA), on hydrolysis behaviors and microstructure with various catalyst for hydrolysis of Ti-tetraisopropoxide was in detail investigated. In case of TiO2 powder with HMPA as an additive, the crystallinity of TiO2 except with NH4OH as a catalyst decreased in XRD patterns, compared to those of products with no additive and with DEG as an additive. The addition of HMPA prohibited the growth of TiO2 and led to fine TiO2 with the average particle size of approximately 10nm.

Enantioselective synthesis of 2-substituted-1,4-diketones from ( S)-mandelic acid enolate and α,β-enones

An approach for the synthesis of chiral non-racemic 2-substituted-1,4-diketones from ( S)-mandelic acid and α,β-enones has been developed. The reaction of lithium enolate of the 1,3-dioxolan-4-one derived from optically active ( S)-mandelic acid and pivalaldehyde with α,β-unsaturated carbonyl compounds proceeds readily to give the corresponding Michael adducts in good yields and with high diastereoselectivities. The addition of HMPA (3 equiv) reverses and strongly enhances the diastereoselectivity of the reaction. A change in the reaction mechanism from a lithium catalyzed to the one where catalysis has been suppressed by coordination of HMPA to lithium is proposed to explain these results. Subsequent basic hydrolysis of the 1,3-dioxolan-4-one moiety yields the corresponding α-hydroxy acids (in hemiacetal form), which after decarboxylation with oxygen in the presence of pivalaldehyde and the Co(III)Me 2opba complex as catalyst give chiral 2-substituted 1,4-dicarbonyl compounds with very high enantiomeric excesses. In this approach, ( S)-mandelic acid acts as an umpoled chiral equivalent of the benzoyl anion.

Anion Relay Chemistry: An Effective Tactic for Diversity Oriented Synthesis

An effective one-flask multicomponent linchpin coupling protocol employing the concept of anion relay chemistry (ARC) was developed. This concept calls for addition of an anion (5) to an epoxide (6), bearing on a distal carbon a trialkyl silyl group and an anion stabilizing group (ASG), to furnish upon epoxide ring opening oxyanion 7. Addition of HMPA or other polar solvents to trigger a solvent controlled 1,4-Brook rearrangement then leads to a new distal anion (8), which in turn is available to react with a variety of second electrophiles.

Synthesis of Oxazolidinones and 1,2‐Diamines from N‐Alkyl Aziridines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Oxazolidinones and 1,2-Diamines fromN-Alkyl Aziridines

Reactions of N-alkyl-substituted aziridines with LiI followed by an electrophile are discussed. In the first series of reactions, the electrophile is carbon dioxide and the product is an oxazolidinone. In all cases, either no reaction occurred or a high yield of product was obtained. HMPA had to be added to some reactions to dramatically improve the regiochemistry. Net retention of stereochemistry was observed. In the second series of reactions, the electrophile is an iminium salt and the product is a 1,2-diamine. Here the reaction is highly regioselective in THF without the addition of HMPA. Unlike the oxazolidinone chemistry, the diamine formation works equally well with or without the addition of LiI. With respect to the regiochemistry, the results are the same with and without added LiI. However, with respect to the stereochemistry, in the presence of added LiI, the reaction with the iminium salt goes with net retention of stereochemistry. In contrast, with no added LiI, in some cases the reaction goes with net retention and in some cases with net inversion of stereochemistry.

Radical Cyclization by Ipso Substitution of the Methoxy Group: Considerable Effect of HMPA on Samarium‐Mediated Cyclization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Radical cyclization by ipso substitution of the methoxy group: considerable effect of HMPA on samarium-mediated cyclization.

Alkyl radicals generated by treatment of thiocarbamates of conformationally favorable 3-alkyl-3-arylpropan-1-ols with tris(trimethylsilyl)silane and AIBN efficiently undergo intramolecular ipso substitution of the methoxy group, yielding the corresponding cyclized products. In contrast, either conformationally favorable or flexible 1-arylalkan-3- or 4-ones easily cyclize into five- or six-membered condensed rings by treatment with SmI(2) via ketyl radical intermediates. The addition of HMPA as cosolvent dramatically changes the cyclization mode of the SmI(2)-induced reaction, and the para-cyclization products are exclusively formed. This "HMPA effect" can be rationalized by the strong chelating ability of HMPA with the samarium atom.

Styrene polymerization with ternary neodymium-based catalyst system: effects of catalyst preparation procedures

The ternary catalyst system neodymium phosphate/di- n-butyl magnesium triethyl aluminum complex/hexamethyl phosphoramide (Nd(P 204) 3/MgBu 2·AlEt 3/HMPA) for the polymerization of styrene was examined. The effects of the addition order of each component, the aging time and temperature and the presence of a small amount of styrene during the preparation of the catalyst system on the activity of the catalyst system and the molecular weight of the resultant polymers were investigated. A stable and homogeneous catalyst system which produces polystyrene with narrow molecular weight distributions can be prepared by an alkylation reaction of Nd(P 204) 3 with MgBu 2·AlEt 3 at ambient temperature followed by the addition of HMPA. An introduction of a small amount of styrene during the preparation of the catalysts can further improve their stability.

Anionic Ring-Opening Polymerization of 1,2,2-Trimethyl-1-phenyl-1,2-disilacyclopentane

The anionic ring-opening polymerization of 1,2,2-trimethyl-1-phenyl-1,2-disilacyclopentane took place in THF at 0∼−78°C. The initiators were nBu4NF, PhMe2SiK, and (PhMe2Si)2Cu(CN)Li2. When PhMe2SiK was used, the addition of HMPA was required for the polymerization. The polymerization initiated with (PhMe2Si)2Cu(CN)Li2 showed a living character to some extent. The product polymers contained not only a head-to-tail structure but also head-to-head and tail-to-tail structures, whose amounts were dependent on the initiator: 4% (nBu4NF), 30% (PhMe2SiK), and 12% ((PhMe2Si)2Cu(CN)Li2). These values reflect the efficiency of the phenyl group to stabilize the silyl anion that is the propagating end.

Tert-Butyldimethylsilyldihalomethyllithium as a dihalomethylene dianion synthon. 1,3-Rearrangement and 1,4-rearrangement of silyl group from carbon to oxide

One-pot synthesis of R 1CH(OSiMe 2- t-Bu)CX 2CH(OH)R 2 (X=Cl, Br) successive addition of two different aldehydes (R 1CHO and R 2CHO) has been achieved starting from tert-butyldimethylsilyldihalomethyllithium. Treatment of a THF solution of the title carbanion (X=Cl) with p-MeOC 6H 4CHO or n-BuCHO followed by an addition of HMPA and benzaldehyde gave the corresponding 1,3-diol monosilyl ether in 83% or 45% yield, respectively. The use of oxirane in place of aldehyde as the first electrophile followed by addition of benzaldehyde provided 1,4-diol monosilyl ether.

Chlorotrimethylsilane-Acetonitrile System as a New Promoter for Carbonyl Allylation by Diallyldibutyltin

Abstract Chlorotrimethylsilane combined with acetonitrile has characteristically promoted allylation of carbonyl compounds by diallyldibutyltin to produce a variety of homoallyl silyl ether in good yields, while the addition of HMPA or LiCl disturbed the allylation.

NMR Studies of Five-Coordinate Tin Enolate: An Efficient Reagent for Halo Selective Reaction toward .alpha.-Halo Ketone or .alpha.-Halo Imine

NMR studies of tin enolates (1), in the presence of HMPA, revealed the presence ofa five-coordinate O-stannyl enolate 1(h) which contributes to upfield shifs of Sn peaks in the 119 Sn NMR spectrum and increased coupling constants J( 119 Sn- 13 C), compared with the four-coordinate tin enolate 1(e). The tautomeric equilibrium between C-stannyl ketone 1(k) and O-stannyl enolate 1(e) was changed by the addition of HMPA, the percentage of enol form being increased. The resulting five-coordinate tin enolates 1(h) showed high reactivity and selectivity for halide di- splacement in reactions with α-halo ketones (2). The tin enolates, when coordinated by Bu 4 NBr, effected a selective reaction with α-halo imines (5) to give a variety of γ-imino ketones (6), which were subsequently hydrolyzed to 1,4-diketones or cyclodehydrated to substituted pyrroles (9)

Regioselective Allylation of Ketenes Promoted by SmI2

Abstract Ketenes react with various allylic halides mediated by 2 equiv samarium(II) diiodide (SmI2) to the ketenes to afford allylated ketones in good yields. In the reaction with γ-substituted allylic halides, the regioselectivity is influenced by the olefinic geometry of allylic halides. By using γ-substituted (E)-allylic halides, the allylation proceeds on the less hindered site (α-position) of allylic groups predominantly and the tendency was enhanced by the addition of HMPA.

Stereoselective synthesis of alcohols containing (Z)- and (E)-olefins, dienes, enynes and styrenes: cyclic β-halogeno ether scissions using samarium diiodide as the electron-transfer agent

In contrast to the sodium-mediated ring scission of 2-substituted 3-chloro ethers of the tetrahydrofuran series, samarium diiodide gives olefins of high (E)-stereoselectivity and provides (E)-conjugated and unconjugated dienes, styrenes and enynes in good yield without appreciable over-reduction. Whilst the SmI2 scission of 3-chloro-2-alkyltetrahydropyrans gives(Z)-rich (Z)/(E) olefin mixtures, the 2-(alk-1′-ynyl) members give (Z)-enyne alcohols with high stereoselectivity, providing a valuable complement to the (E)-enyne synthesis employing the tetrahydrofuran series.In electron-transfer scissions using sodium, the stereochemistry of the product alcohols is related to the ground-state conformation of the cis- and trans-pyrans and -furans. The slow SmI2-mediated reactions appear to involve samarium-complexed intermediates aving structures independent of the original conformation, or of the cis- or trans-geometry of the furan or pyran, and it is the transition states from these intermediates that determine the stereochemical outcome.Scissions in the tetrahydrofuran series can be accelerated by addition of HMPA or DMPU with only a little deterioration in stereoselectivity, but in the tetrahydropyran series there are drastic changes in product stereochemistry when DMPU is added. Brief comment is made on the synthesis of tetrahydro-furan and -pyran precursors.

Enantioselective conjugate addition of Grignard reagents to enones catalyzed by chiral cuprate complexes

The enantioselective conjugate addition of Grignard reagents to enones catalyzed by copper (I) complexes with bidentate chiral auxiliary ligands, N,N'-dialkyl-substituted aminotropone iminates has been studied. The enantioselectivity of the reaction was significantly increased by addition of HMPA and silyl reagents