First Example of Organocatalysis by Polystyrene‐Supported PAMAM Dendrimers: Highly Efficient and Reusable Catalyst for Knoevenagel Condensations

Abstract

This paper describes the first use of polystyrene‐supported poly(amidoamine) (PAMAM) dendrimers as heterogeneous basic organocatalysts for carbon–carbon bond formation. Polystyrene‐supported PAMAM dendrimers of first, second and third generations have been used as reusable base catalysts in Knoevenagel condensations of carbonyl compounds with active methylene compounds. The reactions proceed in short periods of time and with 100 % selectivity. This novel catalyst eliminates the use of aromatic and halogenated solvents, as well as complex purification processes. The catalysts can be recycled ten times.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

“…Using only 0.5 mol % of catalyst 34, α,β-unsaturated nitriles were obtained in excellent yield (98%-100%) in ethanol at room temperature. The yields of the products obtained with this catalyst were similar to those obtained with polystyrene-supported PAMAM dendrimers [27] in the same conditions but with the catalyst 34 the reaction time was shorter. The catalyst 34 was recovered by simple filtration and reused up to eight times without loss of catalytic activity.…”

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions

“…It is worth noting that the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate gave us a yield of >99.9% using a reaction mixture ratio of benzaldehyde : ethyl cyanoacetate : Mg3Al-PW12 = 47980 : 71970 : 1 at 60 o C in Vipropanol:Vwater = 2 : 1. Interestingly, the TON can reach as high as 47980 (Table 4, Entry 1), which is the highest reported so far in comparison with other reported catalysts such as VAp in water (TON = 39583, Entry 2), [44] DMAN/SiO2 in ethanol (TON = 10000, Entry 3), [45] polystyrene-supported poly(amidoamine)dendrimer in ethanol (TON = 198, Entry 4), [46] amine-grafted PE-MCM-41 in cyclohexane (TON = 198, Entry 5), [47] and others listed in Table 4. [48][49][50][51][52][53][54][55][56][57][58][59][60] In an effort to confirm the fact that the catalysis is truly heterogeneous, the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate has been selected as an example.…”

Aqueous DABCO, an efficient medium for rapid organocatalyzed Knoevenagel condensation and the Gewald reaction

“…In the framework of our studies on the chemistry of thiopyran-one structure 16 and its heterocyclic analogues, 17 and in continuation of our previous investigation on the development of aqueous mediated procedures, 18,19 we report herein the successful application of a H 2 O/1,4-diazabicyclo[2.2.2]octane (DABCO) * Correspondence: abaee@ccerci.ac.ir medium, which can cause rapid condensation of ketones 1 with malononitrile derivatives 2 to produce the Knoevenagel products 3 within a few minutes (3)(4)(5)(6)(7)(8)(9)(10). The products can be further converted to 2-aminothiophenes 4, either stepwise or in situ, to show the versatility of the method (Scheme).…”

“…Ethyl cyanoacetate showed a slightly slower reaction due to the lower activity it has (entry 2). Other aldehydes behaved in a similar manner and produced high yields of their respective products (entries [3][4][5][6][7][8][9][10][11][12][13][14]. In all reactions with 2b, only geometric E isomers were obtained in high yields within 1-2 min.…”

“…We next applied the conditions to the reactions of 1c-d with 2a-b. Due to the lower reactivities of these 2 ketones, their reactions were completed in slightly longer intervals giving 88%-92% of 3ca-db in 7-10 min (entries [5][6][7][8]. At the end of the reactions, most of the products precipitated spontaneously and could be separated by simple filtration.…”