Search results for "Reagent"

Pyrrole Studies XXVII.1Utilisation of 1-Methyl-2-pyrrolyl Lithium in the Synthesis of 1-Methyl-2-substituted Pyrroles

1982

Abstract Although metallation of 1-substituted pyrroles with alkyl lithium reagents to give the lithiated derivatives has been recorded by several research groups,4–6 only limited use has been made of these derivatives in the synthesis of 1,2-disubstituted pyrroles. Subsequent to ourinitial studies,7 it was reported that tetrahydrofuran was the solvent of choice for the formation of the mono-lithiated pyrrole derivative and that the rate of the metallation was accelerated by the presence of TMEDA.6 We had noted,7 however, that prolonged reaction of n-butyl lithium with 1-methylpyrrole in a 2:1 mixture of tetrahydrofuran:hexaneat ca 18°C in the absence of TMEDA gave 1-methyl-2-pyrrolyl lithi…

Poly(phosphonate)-mediated Horner–Wadsworth–Emmons reactions

2015

A novel, general protocol for a polymer-mediated Horner–Wadsworth–Emmons (HWE) reaction is reported. The polyvalent polymeric reagent was prepared via acyclic diene metathesis (ADMET) polymerization. Homo- and copolymers of reactive poly(phosphonate)s with molecular weights up to 40 000 g·mol−1 and molecular weight dispersities Đ < 2 were successfully synthesized. Subsequent application of these polymers in the HWE reaction to prepare a library of aromatic α,β-unsaturated ketones (chalcons) has proven to be an efficient synthetic pathway to minimize purification efforts, as the polymeric side-product can be removed by simple precipitation. In this paper we also demonstrate for the first tim…

pH-sensitive hydrogel based on a novel photocross-linkable copolymer.

2004

A pH sensitive hydrogel has been prepared by a UV irradiation technique. Starting polymer was the PHM (poly hydroxyethylaspartamide methacrylated) obtained from polyaspartamide (PHEA) partially derivatized with methacrylic anhydride (MA). This new copolymer has been further derivatized with succinic anhydride (SA) to obtain PHM-SA that has been cross-linked by UV irradiation to form a pH sensitive hydrogel. The network, recovered after washing as a powder, has been been characterized by FT-IR spectrophotometry and particle size distribution analysis. Moreover, to have information about water affinity of the prepared sample, swelling measurements have been carried out in aqueous media mimick…

Gold Redox Catalytic Cycles for the Oxidative Coupling of Alkynes

2011

[EN] Au(I)/Au(III) catalytic cycles are catalytically competent to perform the oxidative coupling of alkynes in the homogeneous phase at room temperature and without any protecting atmosphere. Selectfluor as oxidant, wet acetonitrile as solvent, and sodium carbonate as base are the reagents of choice. Both aromatic and alkyl alkynes can be coupled, and mechanistic studies reveal that at least two gold species having different oxidation states are implicated in the key step of the coupling.

Iron‐Catalyzed C( sp 2 )−C( sp 3 ) Cross‐Coupling of Chlorobenzamides with Alkyl Grignard Reagents: Development of Catalyst System, Synthetic Scope, …

2018

Solvent-free ruthenium-catalysed triflate coupling as a convenient method for selective azole-o-C-H monoarylation.

2019

Metal-catalysed ortho-directed C–H functionalization usually faces selectivity issues in the competition between mono- and disubstitution processes. We report herein the ruthenium-catalysed N-directed C–H monoarylation of arylpyrazoles with a selectivity of up to 96% or that generally reaches values above 80%. This selectivity is an effect of solvent-free conditions associated with sulfonate reagents, in the absence of frequently used acidic additives.

d-Glucose as a multivalent chiral scaffold for combinatorial chemistry

2002

Due to their high density of functional groups and their availability in a variety of diastereomeric forms, monosaccharides are considered attractive scaffolds for combinatorial chemistry that allow the attachment and defined spatial alignment of up to five different pharmacophoric groups. For their application in combinatorial syntheses on solid phase, a set of selectively removable hydroxy protecting groups in combination with a cleavable anchor is required. Herein, we report on the construction and use of a versatile multivalent glucose building block for parallel synthesis on the solid phase.

Über tetraaryl-methan-analoga in der gruppe 14

1994

Abstract The title compounds have been synthesized by Grignard reactions or pyrolysis of diplumbanes respectively. The crystal structures of m -Tol 4 Pb and Ph 4 Pb (redetermination) have been determined. All eight compounds (Ph/Tol) 4 (Sn/Pb) are S 4 symmetric and contracted along this unique axis. The 13 C-NMR chemical shifts and the couplings 1 J ( 119 Sn/ 207 Pb 13 C) as well depend additively upon the methyl substituents. The ratios 1 K ( 207 Pb 13 C): 1 K ( 119 Sn 13 C) of the reduced coupling constants are all near to 1.61; a comparison with values from the literature for alkyl, alkenyl and alkinyl substituents is given. The ratio δ( 207 Pb):δ( 119 Sn) results in 2.28. IR (700 dow…

Synthesis of nonracemic α-trifluoromethyl α-amino acids from sulfinimines of trifluoropyruvate

2001

We describe a novel and useful method for the synthesis of nonracemic α-trifluoromethyl α-amino acids (α-Tfm-AAs). Key building blocks are the sulfinimines (S)-1a and (S)-1b, prepared by Staudinger reaction from trifluoropyruvate esters and the chiral N-sulfinyl iminophosphorane (S)-8, which were treated with benzyl, allyl, and alkylmagnesium halides. The resulting diastereomeric N-sulfinyl α-Tfm α-amino esters, 12 and 13, were produced with moderate to good stereoselectivity and yields. When alkyl Grignard reagents were used, stereocontrol became progressively higher with increasing steric bulk, while reversed, though poor, stereocontrol was achieved with benzyl/allyl Grignard reagents. An…

Stereoselectivity in the Addition of Organotitanium Reagents to Carbonyl Compounds

1986

Although great strides have been made in the area of stereoselective C—C bond forming reactions [1], many problems persist. Early studies concerning chemo- selective reactions of organotitanium reagents (Chapter 3) suggested that they might also behave stereoselectively in relevant cases. In fact, the first such observation goes back to 1979 when it was noted that dichlorodi- methyltitanium (2) adds to the ketone 1 in CH2C12 to produce a mixture of tertiary alcohols 4/5 instead of the desired (±) cuparene (3) [2, 3]. The striking aspect of this transformation is the high disastereoselectivity in favor of 4. Methyllithium shows the opposite stereoselectivity (4:5 = 34:66), in line with the s…