1,721,061 research outputs found
SYNTHESIS OF ISOTHIOCYANATES BY REACTION OF AMIDES WITH CARBON-DISULFIDE IN THE PRESENCE OF SOLID POTASSIUM CARBONATE SODIUM-HYDROXIDE MIXTURE
No full textReadily available N-monosubstituted trifluoroacetamides are transformed into isothiocyanates in good yield by reaction, at room temperature, with carbon disulfide in acetonitrile in the presence of anhydrous sodium hydroxide/potassium carbonate basic mixture
Phase Transfer Catalysis
No full textPhase transfer catalysis (PTC) is a powerful tool to carry out organic reactions in a practical fashion, both in laboratory and industrial scale. Significant cost savings and major process improvements can be achieved in reactions performed in water-organic solvent mixtures under PTC conditions. Accordingly, the market of phase transfer catalysts has continuously grown in the past few years reaching 1,000 USD Million size.
Particularly advantageous is the possibility to replace expensive solvents and dangerous bases such as sodium hydride, requiring strictly anhydrous conditions, with aqueous bases and apolar, environmentally friendly and easily recyclable solvents.
During the last decade notable results have been obtained in stereoselective reactions performed in the presence of chiral, non-racemic quaternary ammonium salts. In addition, new avenues have been opened by the use of bulky chiral phosphate anions to generate lipophilic ion pairs enabling the stereoselective construction of important building blocks. Large scale industrial applications of asymmetric PTC have also been described.
The dissemination of PTC concepts has been facilitated by the possibility to visualize the actual transfer of the ion pair to the organic phase as well as its consumption
SYNTHESIS OF 2-AMINO ACIDS VIA SELECTIVE MONO-N-ALKYLATION OF TRICHLOROACETAMIDE BY 2-BROMO CARBOXYLIC ESTERS UNDER SOLID LIQUID PHASE-TRANSFER CATALYSIS CONDITIONS
No full textTETRABUTYLAMMONIUM FLUORIDE - A POWERFUL CATALYST FOR THE REGIOSELECTIVE OPENING OF EPOXIDES WITH THIOLS
No full textTetrabutylammonium fluoride (1) catalyses under mild conditions the opening of epoxides 2a-k with thiols 3-6 to produce the corresponding beta-hydroxy thioethers 7-11 in excellent yields (88-100%) and with high regioselectivity. Furthermore, O-protected glycidols react without any loss of the protective group
REGIOSELECTIVE CONVERSION OF O-PROTECTED GLYCIDOLS TO FLUOROHYDRINS CATALYZED BY TETRABUTYLAMMONIUM DIHYDROGENTRIFLUORIDE UNDER SOLID-LIQUID PTC CONDITIONS
No full textA number of O-protected glycidols are regioselectively converted into the corresponding fluorohydrins FCH2CH(OH)CH2OX by reaction with catalytic amounts of Bu4N+H2F3- and a molar excess of KHF2. Most of the protective groups (X) examined are stable under the above conditions, moreover stereogenic carbons are not affected
Regioselective opening of epoxides to beta-amido alcohols under solid-liquid PTC conditions
No full textA study on the ring opening of a number of epoxides 1 with trifluoroacetamide (2) under solid-liquid phase transfer catalysis (SL-PTC) conditions has been performed. The reaction is completely regioselective affording beta-amido alcohols 3 deriving from the attack of the nucleophile to the less substituted carbon atom of the oxirane ring. (C) 1997 Elsevier Science Ltd
Novel concise synthesis of 2-substituted 3,4-dihydro-2H-1,4-benzoxazines by ring opening of glycidols under solid-liquid phase transfer catalysis conditions
No full textThe ring opening of glycidols with N-(2-fluorophenyl)toluene-p-sulfonamide under SL-PTC conditions, followed by ring closure with (BuOK)-O-t, provides a novel high yielding synthesis of 2-substituted 3,4-dihydro-2H-1,4-benzoxazines
SYNTHESIS OF PENTACOORDINATED TETRAALKYLAMMONIUM AND TETRAALKYLPHOSPHONIUM DIFLUOROSILICATES
No full textSeveral quaternary onium difluorosilicates 3, R(2)(1)R(2)SiF(2)(-) Q(+) (Q = R(3)(3)R(4)N(+), R(3)(3)R(4)P(+)), have been prepared by reaction of a trisubstitued silane I, R(2)(1)R(2)SiH, and an onium hydrogendifluoride 2, Q(+) HF2-, in benzene. The products 3 are isolated in very good yields (92-98%) and purity (> 99%)
REDUCTION OF ALLYLIC NITRO-COMPOUNDS TO OXIMES WITH CARBON-DISULFIDE UNDER SOLID LIQUID PHASE-TRANSFER CATALYSIS CONDITIONS
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