Showing papers on "Alkylation published in 1994"

Toward "Willowlike" Thermotropic Dendrimers

Abstract: The synthesis and characterization of the AB 2 monomers 6-bromo-1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)hexane (8 or TPH-b), 13-bromo-1-(4-hydroxyphenyl)-2-[4-(6-hydroxy-2-naphthalenylyl)-phenyl]tridecane (22 or BPNT-b), and 13-bromo-1-(4-hydroxyphenyl)-2-(4-hydroxy-4''-p-terphenylyl)tridecane (30 or TPT-b) are described. The phase-transfer-catalyzed polyetherification of all monomers followed by in situ alkylation of their phenolate chain ends with bromoalkanes, benzyl chloride, or allyl chloride led to the soluble hyperbranched polymers TPH-b-X, BPNT-b-X, and TPT-b-X (where X refers to the nature of their chain ends, for example, when X= Bz= benzyl, X= All= allyl, and, when X= numeral, it represents the number of carbons in the alkyl chain end)

Process for preparing short chain alkyl aromatic compounds

Abstract: A process for producing alkyl aromatic compounds which comprises contacting at least one aromatic compound with at least one alkylating agent or transalkylating agent possessing at least one aliphatic group having from 1 to 5 carbon atoms under alkylation or transalkylation reaction conditions and in the presence of an alkylation or transalkylation catalyst, to provide an alkylated aromatic product possessing at least one alkyl group derived from said alkylating agent or transalkylating agent, said catalyst comprising a binder-free molecular sieve having an X-ray diffraction pattern that includes the lines set forth in Table A

SN2'-Reactions of Peptide Aziridines. A Cuprate-Based Approach to (E)-Alkene Isosteres

Abstract: Alkenylaziridines were prepared from allylic alcohols via Sharpless epoxidation, oxirane to aziridine conversion under modified Staudinger conditions, and Wittig chain extension. Alternatively, β-hydroxy α-amino acids such as threonine can serve as readily available precursors. The corresponding N-acyl, -peptidyl-, -carbamoyl-, and -sulfonylaziridines underwent a high-yielding anti-S N 2' alkylation with organocopper/BF 3 complex to give (E)-alkene peptide isosteres in 62 to >98% de. The stereoselectivity of the addition process was studied by 1 H and 19 F NMR as well as chemical degradation. Alkene isosteres are important nonhydrolyzable and rigidified analogs of peptide bonds in biologically active peptides. This new methodology considerably facilitates the synthesis and the study of these peptide mimetics, since alkenylaziridines are readily prepared and side-chain modification is simplified by the wide range of functionalized organocopper reagents that are available

(+)- and ent-(-)-Duocarmycin SA and (+)- and ent-(-)-N-BOC-DSA DNA Alkylation Properties.Alkylation Site Models That Accommodate the Offset AT-Rich Adenine N3 Alkylation Selectivity of the Enantiomeric Agents

Abstract: A detailed study of the DNA alkylation properties of (+)-duocarmycin SA, ent-(-)-duocarmycin SA, and (+)- and ent-(-)-N-BOC-DSA (2) is described, and the development of a model that accommodates the offset AT-rich adenine N3 alkylation selectivity of the enantiomeric agents is presented

A comparative study of O42− /ZrO2 and zeolite beta as catalysts for the isomerization of n-butane and the alkylation of isobutane with 2-butene

Abstract: The activity, selectivity, and decay behavior of SO2−/ ZrO2 (SZ) and zeolite Beta (Hβ) catalysts are compared for two acid catalyzed demanding reactions, i.e., the isomerization of n-butane, and the alkylation of isobutane with 2-butene. The superacidity present in the SZ sample makes this catalyst active for both reactions at lower temperatures than the zeolite. For the isomerization of n-butane the reaction pathway leading to isobutane was seen to be different for both catalysts. A similar decay behavior was observed on the two catalysts, but the SZ sample gave a much higher selectivity to isobutane. For the alkylation reaction, the SZ catalyst is much more selective to TMP's than Hβ at low reaction temperatures. The lower selectivity to TMP's obtained on Beta zeolite is mainly due to the formation of DMH's by dimerization of butenes, while undesirable cracking reactions leading to C5-C7 products occur to a higher extent on the superacid SZ catalyst. The latter deactivates much faster than the zeolite. The acid strength distribution, and hydrogen transfer activity were seen to determine the changes in product distribution with time-on-stream obtained on both catalysts.

Asymmetric synthesis of anti-α-alkyl-β-amino acids

Abstract: An investigation into the asymmetric induction accompanying alkylations of enolates derived from the highly diastereoselective conjugate addition of lithium (R)-N-benzyl-N-α-methylbenzylamide (R)-1 to crotonate and cinnamate esters has been performed. The access to different enolate geometries afforded by the conjugate addition process and subsequent enolate regeneration by deprotonation of the β-amino ester conjugate adducts enabled two disparate sets of selectivity data to be compiled. Although both approaches furnished predominantly anti-α-alkyl-β-amino esters, the two-step procedure proved to be considerably more selective. Several factors which play a major role in determining the alkylation selectivity are identified, including the cooperative influence of the α-methylbenzylamino stereocentre. Since debenzylation and hydrolysis of the alkylated products was straightforward, this methodology provides a direct route to anti-α-alkyl-β-amino acids in homochiral form.

Chemistry of Cyclic Tautomers of Tryptophan: Formation of a Quaternary Center at C3a and Total Synthesis of the Marine Alkaloid (+)-ent-Debromoflustramine B

Abstract: A diastereoselective synthesis of the unnatural (+)-enantiomer of the marine alkaloid (-)-debromoflustramine B (1) from a cyclic tautomer (9) of L-tryptophan is described. The optical rotation of the synthetic 1 is opposite to that of the natural material enabling the configuration of the natural product to be established as 3aS,8R. As natural flustramine B has been converted to (-)-debromoflustramine B its absolute configuration may also be set as 3aS,8aR. The synthetic scheme involves radical bromination of 9 at C3a followed by allylation, at C3a, with allyltributyltin to give 21. The allyl group is then converted to the C3a prenyl derivative 23 by oxidative cleavage and Wittig reaction. The remainder of the synthesis involves removal of the now extraneous carbomethoxy group from C2 and selective removal of the two nitrogen protecting groups and alkylation of the resulting amines. Oxidation of 9 with ceric ammonium nitrate to give mixtures of the C3a nitrato- and hydroxy-derivatives 18 and 19 is also described

Asymmetric synthesis mediated by chiral ligands

Abstract: Chiral chelated lithium amides were designed and synthesized. Studies have been done to explore the use of these lithium amides or their corresponding amines for enantioselective reactions such as deprotonation of prochiral cyclic ketones, kinetic resolution of racemic 2-substituted cyclohexanones by deprotonation, regioselective deprotonation of optically active 3-keto steroids, alkylation of achiral ketones, and deracemization of chiral ketones by protonation. Approaches to catalytic asymmetric deprotonation and alkylation are also attempted.

Asymmetric Alkylations of a Sultam-Derived Glycine Equivalent: Practical preparation of enantiomerically pure α-amino acids

Abstract: Alkylation of the chiral glycine derivative 2 with “activated” organohalides under ultrasound-assisted phasetransfer catalysis or with activated and nonactivated organohalides in anhydrous medium provides (mostly crystalline) alkylation products 3. Acidic hydrolysis of the pure products 3 gives (aminoacyl)sultams 4 which by mild saponification furnish pure α-amino acids 5 in good overall yields from 2, along with recovered auxiliary 1 (Scheme 1). Pure ω-protected α,ω-diamino acids and α-amino-ω-(hydroxyamino)acids 12–16 are readily accessible from (ω-haloacyl)sultams 3via reaction with N-nucleophiles followed by acidic and basic hydrolyses (Scheme 2). A reliable determination of the enantiomeric purity of α-amino acids using HPLC analysis of their N-(3,5-dinitrobenzoyl)prolyl derivatives 17 is presented.

2,3-Pyrrolidinedicarboxylates as Neurotransmitter Conformer Mimics: Enantioselective Synthesis via Chelation-Controlled Enolate Alkylation

Abstract: Conformationally restricted analogs of naturally-occurring amino acids can serve in a variety of ways as protein structure/function probes. A diastereo- and enantioselective synthesis of the four stereoisomers of 2,3-pyrrolidinedicarboxylic acid (an analog of aspartic acid) are described in this paper. The key step is a Rapoport-type aspartate alkylation that can be controlled to give good yields of either diastereomer as a function of enolate geometry. A novel type of chelation control is proposed to account for these results

Rhodium-catalysed regioselective alkylation of the phenyl ring of 2-phenylpyridines with olefins

Abstract: 2-Phenylpyridines react with olefins react with olefins in the presence of rhodium(I) as a catalyst to give 2-(2-alkylphenyl)pyridines by a regioselective alkylation at the ortho position of the phenyl ring.

Zeolite beta as a catalyst for alkylation of isobutane with 2-butene. Influence of synthesis conditions and process variables

Abstract: The continuous alkylation of isobutane with 2-butene was carried out on a series of beta catalysts prepared by two different synthesis procedures, involving the use of amorphous silica (Aerosil) and TEOS as silica source. The stability of the zeolite towards dealumination during the activation steps was seen to increase with Si/Al ratio and crystal size of the beta catalyst. The most stable catalysts were also the most active and selective for alkylation, giving a higher TMP/DMH ratio during the initial reaction stages. These samples also deactivate at a lower rate with TOS. The observed differences in catalytic activity and selectivity were attributed to differences in both total acidity and acid strength distribution. Finally, the influence of reaction temperature and isobutane/2-butene ratio on the catalytic behavior were also investigated.

Alkylation of isobutane with butenes over solid superacids, SO42−/ZrO2 and SO42−/TiO2

Abstract: Solid superacids SO42−/ZrO2 and SO42−/TiO2 were applied in the alkylation of isobutane with butenes at a reaction temperature of 100° C. They showed high activity, selectivity and stability. The nature of the superacid sites was discussed based on IR, X-ray diffraction, and measurement of the acidic properties of the catalyst. An amorphous support was essential for preparing effective catalysts. The optimal calcination temperatures were 650°C and 550°C for SO42−/ZrO2 and SO42−/TiO2, respectively. The catalytic activity correlates well with the acid strength of the catalyst. Activation of isobutane over the solid superacid was observed at 100° C.

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

Abstract: The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 25 MPa total pressure, and a variety of olefin space velocities At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Bronsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels At short times on stream (TOS), TMP's account for ca 40% of the C8 fraction The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores

Asymmetric synthesis of syn-α-alkyl-β-amino acids

Abstract: An investigation into the reactivity of the highly stereoselective conjugate nucleophile lithium N-benzyl-N-α-methylbenzylamide 1 with α-alkyl-α,β-unsaturated esters has led to the development of a versatile asymmetric synthesis of syn-α-alkyl-β-amino acids. By performing the conjugate additions in toluene and diluting the reaction mixtures with THF prior to quenching of the reactions with the hindered acid, 2,6-di-tert-butylphenol 13, the product syn-α-alkyl-β-amino esters may be generated in good yield and with excellent stereocontrol. Several examples illustrate the ease with which these products may be debenzylated and hydrolysed to afford homochiral syn-α-alkyl-β-amino acids.

Effect of pore size and aluminium content on the production of linear alkylbenzenes over HY, H-ZSM-5 and H-ZSM-12 zeolites: Alkylation of benzene with 1-dodecene

Abstract: H-ZSM-5 (Si/Al = 15 and 30), H-ZSM-12 (Si/Al = 80) and HY zeolites (Si/Al ratios in the range 2.7-26.4) were evaluated in the benzene alkylation reaction with 1-dodecene for linear alkyl-benzene-LAB production. A series of dealuminated Y-zeolites was prepared under strictly controlled conditions by treatment with silicon tetrachloride. The materials thus obtained were washed and exchanged with ammonium chloride. The catalysts were characterized by X-ray diffraction, infrared spectroscopy of the framework vibrations,29Si and27Al-nuclear magnetic resonance. Temperature-programmed desorption of ammonia and elemental analysis. H-ZSM-5 and H-ZSM-12 catalysts showed very low activity. H-ZSM-12 zeolite exhibits both product and transition state type shapeselectivity, favouring the formation of the least bulky 2-phenyl isomer. With HY-zeolites, the alkylation activity increased linearly with the number of lattice Al per unit cell over a range of Si/Al ratios from 2.7 to 26.4, so a practically constant turnover frequency is obtained. The HY-zeolites also gave 97–98% selectivity towards LAB and produced branched dodecene, traces of branched alkylates and dialkylbenzenes as by-products. Neither dialkyltetralins nor dialkylindanes were found among the products. HY-zeolites did not exhibit shape-selectivity effects. The apparent activation energy was 15 kcal/mol. Small changes in the low Na content of the zeolites were responsible for considerable increases in activity. Dealuminated HY zeolites showed the highest selectivity towards 2-phenyldo-decane. In this case we suggest that the alkylation reaction competed effectively with the migration of the double bond across the chain, so that some of the initial alkylcarbenium ions formed alkylated benzene without undergoing isomerization. The isomerization of the phenylalkane was not observed after alkylation.