Novel Basic Mesoporous Catalysts for the Friedländer Reaction from 2-Aminoaryl Ketones: Quinolin-2(1H)-ones versus Quinolines (original) (raw)
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Chemistry, an Asian journal, 2012
The acid-catalyzed Friedel-Crafts reaction of alcohols and electron-rich aromatic compounds is a highly atom-efficient method for the preparation of aromatic compounds with diverse applications, and only water is generated as the byproduct. During the past decade, significant progress has been made in the development of a catalytic version of this transformation, including the construction of hindered allcarbon quaternary centers. Generally, carbenium ions are invoked as intermediates in this SN 1 -type reaction, and substituents that can stabilize the intermediates could facilitate this reaction ( ). Accordingly, most of the known catalytic protocols are based on alcohols with electron-donating groups that could stabilize the intermediate carbocations. The limited catalytic arylation reactions of alcohols with an a-electron-withdrawing substituent have been restricted to alcohols that could form reactive oxonium [3e] or vinylogous iminium [3f-k] intermediates. If the catalytic Friedel-Crafts arylation reaction could be extended to alcohols with an a-electron-withdrawing group such as a-hydroxyesters or a-hydroxyketones, it would provide a facile method for the a-arylation of esters and ketones. However, to the best of our knowledge, the catalytic version of this reaction has not been reported. The a-quaternary carbonyl compounds, especially a-diaryl or a-triaryl-substituted carbonyl compounds, have wide applications in organic synthesis, medicinal research, and catalyst design. However, synthetic methods to afford these building blocks are very limited, and they often involve multistep synthesis. For example, triarylacetic acid derivatives were often prepared by the reaction of CO 2 and organolithium compounds derived from triarylmethyl chlorides, which were obtained from the corresponding a-triaryl-substituted tertiary alcohols. [6b] Therefore, the development of efficient methods for the diverse synthesis of these compounds is highly desirable.
The scope and limitations of metal salt Lewis acid catalysts were examined for the selectivity control for the formation of Friedländer and non-Friedländer product during the reaction involving 2-aminobenzophenone and ethyl acetoacetate. From a pool of metal halides, tetrafluoroborates, perchlorates, and triflates used as catalyst, In(OTf)3 emerged as the most effective catalyst for selective/exclusive formation of the Friedländer product. The generality of the In(OTf)3-catalysed Friedländer reaction was demonstrated by the reaction of differently substituted 2-aminoarylketones with various carbonyl compounds containing active methylene group (e.g., β- ketoesters, cyclic/acyclic β-diketones, cyclic/acylic ketones, and aryl/heteroaryl methyl ketones) under solvent-free conditions affording the desired quinolines in 75-92% yields.
Different Keggin type heteropoly acids (HPAs) and supported ones on solids with different nature and textural properties were used in the Friedländer reaction in order to obtain quinoline derivatives. This conversion has been preceded by tungstophosphoric acid supported on silica, KSF and activated carbon as optimized catalysts in high yields and short reaction times. The general applicability of this method is demonstrated by using various substrates including ketones, b-ketoesters and b-diketones. For most substrates the reaction worked well. These catalysts were found to be reusable and considerable catalytic activity could still be achieved after the fourth run.
South African journal of chemistry, 2011
Different Keggin type heteropoly acids (HPAs) and supported ones on solids with different nature and textural properties were used in the Friedländer reaction in order to obtain quinoline derivatives. This conversion has been preceded by tungstophosphoric acid supported on silica, KSF and activated carbon as optimized catalysts in high yields and short reaction times. The general applicability of this method is demonstrated by using various substrates including ketones, b-ketoesters and b-diketones. For most substrates the reaction worked well. These catalysts were found to be reusable and considerable catalytic activity could still be achieved after the fourth run.
A New Green Approach to the Friedländer Synthesis of Quinolines
Synlett, 2003
A new approach to the Friedländer synthesis of quinolines is described. Polysubstituted quinolines are readily prepared under milder conditions than in other existing methods through a gold(III)-catalysed sequential condensation/annulation reaction of o-amino aromatic carbonyls and ketones containing active methylene groups.
Catalysts for Fine Chemical Synthesis Volume 1
John Wiley & Sons, Ltd ISBN: 0-471-98123-0, 2002
During the early-to-mid 1990s we published a wide range of protocols, detailing the use of biotransformations in synthetic organic chemistry. The procedures were first published in the form of a loose-leaf laboratory manual and, recently, all the protocols have been collected together and published in book form (Preparative Biotransformations, Wiley-VCH, 1999). Over the past few years the employment of enzymes and whole cells to carry out selected organic reactions has become much more commonplace. Very few research groups would now have any reservations about using commercially available biocatalysts such as lipases. Biotransformations have become accepted as powerful methodologies in synthetic organic chemistry. Perhaps less clear to a newcomer to a particular area of chemistry is when to use biocatalysis as a key step in a synthesis, and when it is better to use one of the alternative non-natural catalysts that may be available. Therefore we set out to extend the objective of Preparative Biotransformations, so as to cover the whole panoply of catalytic methods available to the synthetic chemist, incorporating biocatalytic procedures where appropriate In keeping with the earlier format we aim to provide the readership with sufficient practical details for the preparation and successful use of the relevant catalyst. Coupled with these specific examples, a selection of the products that may be obtained by a particular technology will be reviewed. In the different volumes of this new series we will feature catalysts for oxidation and reduction reactions, hydrolysis protocols and catalytic systems for carbon–carbon bond formation inter alia. Many of the catalysts featured will be chiral, given the present day interest in the preparation of single-enantiomer fine chemicals. When appropriate, a catalyst type that is capable of a wide range of transformations will be featured. In these volumes the amount of practical data that is described will be proportionately less, and attention will be focused on the past uses of the system and its future potential. Newcomers to a particular area of catalysis may use these volumes to validate their techniques, and, when a choice of methods is available, use the background information better to delineate the optimum strategy to try to accomplish a previously unknown conversion
New heterogeneous catalysts for greener routes in the synthesis of fine chemicals
Journal of Catalysis, 2007
New strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated to previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Following these procedures, catalysts with different Si/Sn ratios-21.8 to 50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7-were prepared. These new materials were tested in the acylation of aromatic sulfonamides using acetic acid as the acylating agent and in the synthesis of (dl)-[α]-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP). The activity data indicate that these heterogeneous catalysts are very active, corresponding to high yields in acylated compounds as 65.5% and very high selectivity to (dl)-[α]-tocopherol (94%, for a conversion of 98%).