Showing papers on "Alkylation published in 1999"
TL;DR: A statistical survey of industrial processes using solid acid-base catalysts is presented in this paper, where the number of processes such as alkylation, isomerization, amination, cracking, etherification, etc.
Abstract: A statistical survey of industrial processes using solid acid–base catalysts is presented. The number of processes such as alkylation, isomerization, amination, cracking, etherification, etc., and the catalysts such as zeolites, oxides, complex oxides, phosphates, ion-exchange resins, clays, etc., are 127 and 180, respectively. The classification of the types of catalysts into solid acid, solid base, and solid acid–base bifunctional catalysts gives the numbers as 103, 10 and 14, respectively. Some significant examples are described more in detail. On the basis of the survey, the future trend of solid acid–base catalysis and the fundamental research promising for industrial success are discussed.
972 citations
228 citations
TL;DR: In this article, an attempt is made to rationalize, on a mechanistic basis, the selectivity loss almost always encountered with solid acids after relatively short times on-stream, and suggestions are made concerning a more target-oriented research on isobutane/alkene alkylation in the future.
164 citations
Journal Article•
TL;DR: An overview of the spontaneous chemistry of cyclophosphamide metabolites can be found in this paper, where perturbations to metabolite distributions and half-lives effected by buffer, structure, pH and nucleophiles are discussed.
Abstract: This is primarily an overview of the spontaneous (non-enzymatic) chemistry of the metabolites of cyclophosphamide, viz., cis- and trans-4-hydroxycyclophosphamide, aldophosphamide (and its hydrate), iminophosphamide, phosphoramide mustard, acrolein, and chloroethylaziridine. A brief description of detoxification products obtained through enzyme catalyzed reactions appears. Included as the historical basis for the development of cyclophosphamide is the chemistry of nitrogen mustards. Among the topics covered are: perturbations to metabolite distributions and half-lives effected by buffer, structure, pH and nucleophiles; effects of pH on mechanism; alkylation versus P-N bond hydrolysis; the influence of nucleophiles on alkylation product distributions; the influence of substituents on alkylation rates; and preactivated forms of cyclophosphamide as metabolite precursors (4-hydroperoxycyclophosphamide and mafosfamide). A review with 66 references.
161 citations
TL;DR: In this article, the lithium salts of the ligands ArNC(R)CHC (R)NAr, where Ar = 2,6-Pri-C6H3 and R = CH3 and But, gave LScCl2·nTHF derivatives (R = CH 3, n = 1, 1a; R = But, n= 0, 1b).
158 citations
TL;DR: (5-pyrimidyl)alkanol with a tert-butylethynyl group at its 2-position is a very efficient asymmetric autocatalyst in the enantioselective alkylation in Equation (1).
Abstract: Extremely high enantioselectivity (>99.5% ee) and chemical yield (>99%) are achieved in an asymmetric autocatalytic reaction. A (5-pyrimidyl)alkanol with a tert-butylethynyl group at its 2-position (1) is a very efficient asymmetric autocatalyst in the enantioselective alkylation in Equation (1).
149 citations
TL;DR: The silica-included heteropolyacid is a microporous material with a sharp pore-size distribution around 0.55 nm and showed shape selective acid catalysis in the alkylation of phenol with formaldehyde giving a higher yield of 4,4′-dihydroxydiphenylmethane isomer.
Abstract: Freely water-soluble 12-tungstophosphoric acid could be made insoluble through immobilization inside a silica matrix by means of sol–gel technique involving hydrolysis of tetraethyl orthosilicate. The silica-included heteropolyacid thus obtained catalyzed the water-participating reactions of esterification and isobutene hydration more efficiently than the resin catalyst of Amberlyst-15 and the zeolite H-ZSM-5. The silica-included heteropolyacid is a microporous material with a sharp pore-size distribution around 0.55 nm, and it showed shape selective acid catalysis in the alkylation of phenol with formaldehyde giving a higher yield of 4,4′-dihydroxydiphenylmethane isomer.
134 citations
TL;DR: It was found that the magnesium-mediated allylation of aldehydes with allyl bromide and iodide proceeds effectively in aqueous 0.1 N HCl or 0.
Abstract: Magnesium-mediated Barbier−Grignard type alkylation of aldehydes with alkyl halides was studied in aqueous media. The reaction of aromatic aldehydes with allyl halides is highly effective with either THF or water as the reaction solvent but poor in a mixture of THF/water. It was found that the magnesium-mediated allylation of aldehydes with allyl bromide and iodide proceeds effectively in aqueous 0.1 N HCl or 0.1 N NH4Cl. Aromatic aldehydes reacted chemoselectively in the presence of aliphatic aldehydes. An exclusive selectivity was also observed when both aliphatic and aromatic aldehyde functionalities are present in the same molecule. In the absence of allyl halides, aldehydes and ketones reacted with magnesium in aqueous 0.1 N NH4Cl to form the corresponding pinacol coupling products in high yields. The effectiveness of the pinacol reaction was strongly influenced by the steric environment surrounding the carbonyl group. Aliphatic aldehydes and simple alkyl halides appear inert under the reaction condi...
125 citations
TL;DR: In this article, conditions were found for alkylating oxazaborolidinone enolates derived from phenylalanine (5, 33), alanine (18, 26), phenylglycine (43), and valine (54) without significant loss of boron configuration.
Abstract: Oxazaborolidinones 3, 25, 32, 42, 49, and 53 can be obtained as single diastereomers by crystallization-induced asymmetric transformation (AT). Asymmetric memory is maintained in the derived enolates because the stereogenic boron resists equilibration with achiral, trivalent boron-containing species on the time scale of enolate alkylation with methyl iodide, allyl bromide, or benzyl bromide. Conditions were found for alkylating oxazaborolidinone enolates derived from phenylalanine (5, 33), alanine (18, 26), phenylglycine (43), and valine (54) without significant loss of boron configuration. The phenylglycine-derived oxazaborolidinone alkylation products 44 and 45 slowly undergo boron epimerization at room temperature, and the C-allyl product 44b partially racemizes during hydrolytic cleavage, apparently by a 2-aza-Cope rearrangement. These complications were not encountered with phenylalanine derivatives. Preparatively useful results were obtained with oxazaborolidinones 3 and 32, derived from phenylalani...
114 citations
TL;DR: Curtius rearrangement of the resulting carboxylic acid provided the enantiopure benzyloxycarbonyl (Cbz)-protected β-amino esters 6 in good yields (74−79%).
Abstract: A general procedure for the synthesis of enantiopure β-substituted, β-amino acids is presented. Alkylation of the sodium enolates derived from chiral N-acyloxazolidinone imides 2 (R = Me, i-Pr, t-Bu, Ph, Bn) with tert-butyl bromoacetate afforded the 2-substituted succinate derivatives 3 in good yields (82−89%) and with high selectivity (≥93:7). Following hydrolysis, Curtius rearrangement of the resulting carboxylic acid provided the enantiopure benzyloxycarbonyl (Cbz)-protected β-amino esters 6 in good yields (74−79%).
110 citations
TL;DR: In this article, a 2-phosphorylation of 1-alkyl substituted imidazoles with P(III) halides in pyridine was shown to proceed at the 3-N atom of the heteroaryl ring and was followed by triethylamine-in-duced migration of the phosphorus group to the 2-C atom.
Abstract: Phosphorylation of 1-alkyl substituted imidazoles and benzimidazoles with P(III) halides in pyridine was shown to proceed at the 3-N atom of the heteroaryl ring and was followed by triethylamine-in- duced migration of the phosphorus group to the 2-C atom. Preparative methods were developed for the syn- thesis of a range of 2-phosphorylated derivatives of the indicated imidazoles. The latter were found to undergo alkylation either at P(III) or 3-N centers, depending on the alkylating agent. q 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 585-597, 1999
TL;DR: The approach to medium ring ethers utilized in this synthesis provides a general and efficient route to the cyclic core of other marine natural products.
TL;DR: In this article, N-anthracenylmethyl dihydrocinchonidinium bromide was used as a catalyst for the enantioselective alkylation of a series of alanine-derived imines.
TL;DR: In this paper, the palladium complexes coordinated with the chiral monophosphines are highly effective catalysts for catalytic asymmetric allylic substitution reactions, where chelating bisphosphine ligands cannot be used because of their low catalytic activity or low selectivity towards the desired reaction pathway.
TL;DR: In this paper, a one pot selective mono N-alkylation of primary amides, thioamides, carbamates and ureas has been developed using aromatic and aliphatic aldehydes as alkylating agents and rifluoroacetic acid triethylsilane as reagents.
TL;DR: In this paper, two mesoporous silica-aluminas (MSA and MCM-41) were compared with the amorphous microporous silicas-alumina (ERS-8) and the zeolite beta in the liquid-phase alkylation of toluene with propylene.
TL;DR: The main source of these effects is the decrease in the outer sphere solvation energy induced by the N -alkylation as mentioned in this paper, which is the major source of the N-alkylization of amine ligands.
TL;DR: In this paper, a large pore, crystalline aluminosilicate has been employed as a catalyst for several industrially important reactions, such as benzene isopropylation to cumene, transalkylation and disproportionation of C7 and C9 aromatic streams to produce xylenes.
Abstract: A highly siliceous, large pore, crystalline aluminosilicate has been employed as a catalyst for several industrially important reactions. These reactions include benzene isopropylation to cumene, isopropylation of toluene to cymene, cumene alkylation to diisopropyl benzene, transalkylation and disproportionation of C7 and C9 aromatic streams to produce xylenes and meta-xylene isomerisation in the presence of ethylbenzene. Beta zeolite selectively catalyses benzene alkylation to cumene and formation of n-propyl benzene has been almost eliminated. Beta zeolite was found to be selective for cymenes and diisopropyl benzene formation. The alkylation activity of zeolite beta for cumene isopropylation can be stabilised by steaming and treatment with (NH4)2SiF6. In disproportionation and transalkylation over large pore beta zeolite the xylene yields were found to be better as compared to that of medium pore zeolites. Beta zeolite appears to be quite promising a candidate for several commercial applications.
TL;DR: New Pd(0) olefin complexes, 2−5, of a binaphthalene-based chiral P,N(oxazoline) auxiliary, (S,R)-2-[4-(isopropyl)oxazol-2-yl]-2‘-diphenylphosphino-1,1'binaphthyl, 1, have been prepared as discussed by the authors.
TL;DR: In this article, a new synthesis of vinylarenes selectively substituted in both their ortho positions with different alkyl groups is reported, starting from ortho -alkyl substituted iodoarenes which are caused to react with aliphatic iodides, terminal olefins, K 2 CO 3, AcOK and Pd(OAc) 2 in a one-pot reaction consisting of a series of elementary steps controlled by palladium in its oxidation states 0, II and IV.
TL;DR: In this article, the authors compared the early data with a pseudo first order law in dodecene and found that the selectivity to the most desired 2-phenyl dodecane isomer was increased with increased porous constraints.
Abstract: LAB (Linear Alkyl Benzene) isomers were obtained by the alkylation of benzene with 1-dodecene over FAU, BEA and EMT zeolites in the presence of decane as solvent. The initial activities were compared by fitting the kinetics early data with a pseudo first order law in dodecene. These were in agreement with those determined from the slope of the conversion versus time curve at zero conversion. The activity and stability were discussed in terms of the residual Na + content, Si/Al ratio and porous structure of the catalysts. The selectivity to the most desired 2-phenyl dodecane isomer was found to increase with increased porous constraints. Yields in the preferred isomer over BEA catalysts were very close to those provided by the FAU open structure catalysts in spite of a much lower conversion over BEA catalysts. Deactivation affected not only the alkylation reaction, but the isomerisation of the olefin as well, over BEA catalysts.
TL;DR: Current studies of the zinc metalloenzyme protein farnesyltransferase have shed light on its structure and catalytic mechanism, as well as the general mechanism of zinc-catalyzed sulfur alkylation.
TL;DR: Chiral oxazolidines 2a−e can be diastereoselectively alkylated with BrCF2CO2Et to furnish 3,3-difluoroazetidin-2-ones with up to 99% de as mentioned in this paper.
Abstract: Chiral oxazolidines 2a−e can be diastereoselectively alkylated with BrCF2CO2Et to furnish 3,3-difluoroazetidin-2-ones 3a−e with up to 99% de. Selective cleavage of the chiral appendage provided the corresponding unsubstituted azetidinones. Formation of optically pure α,α-difluoro-β-amino acids 5a−c can be achieved by acidic hydrolysis of N-vinyl-azetidin-2-ones.
TL;DR: In this paper, a selective N-alkylation of primary amines was developed using cesium hydroxide to prepare various secondary amines efficiently, and the preliminary results demonstrated that this methodology was highly chemoselective, favoring mono-N-alkylation over dialkylation.
TL;DR: In this article, 1-propanol was used for the alkylation of 2-propylphenol and 3-pentanone in a CeO2-MgO catalyst.
TL;DR: Gas phase conditions were successfully used for fine chemistry, in the N-alkylation of amines with alcohols as alkylating agents and γ-alumina as a catalyst as discussed by the authors.
TL;DR: In this article, N -anthracenylmethyl dihydrocinchonidinium bromide quaternary ammonium phase-transfer catalysts were used for the enantio and diastereoselective synthesis of bis-α-amino acid esters.
TL;DR: A modified procedure for the synthesis of highly enantiomerically enriched alpha-amino acids is described that involves the direct alkylation of pseudoephedrine glycinamide hydrate followed by hydrolysis.
Abstract: A modified procedure for the synthesis of highly enantiomerically enriched α-amino acids is described that involves the direct alkylation of pseudoephedrine glycinamide hydrate (1·H2O) followed by hydrolysis. The modified procedure was developed to overcome several inconvenient aspects of our earlier reported procedure. Advantages of the new method include (1) a greatly simplified one-step synthesis of the alkylation substrate (1·H2O) by the direct combination of glycine methyl ester hydrochloride with pseudoephedrine in the presence of lithium tert-butoxide, (2) the use of the weaker base lithium hexamethyldisilazide (LHMDS) in lieu of lithium diisopropylamide (LDA) for the enolization reaction, (3) a protocol for the direct alkylation of 1·H2O without the need for prior drying of the alkylation substrate, and (4) a one-step alkylation procedure that generates LHMDS and anhydrous lithium chloride simultaneously from the reaction of lithium metal with n-hexyl chloride in the presence of hexamethyldisilazane.