2018
DOI: 10.1016/j.carbpol.2018.07.009
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Preparation of chitosan-supported urea materials and their application in some organocatalytic procedures

Abstract: An efficient and mild procedure was developed for the preparation of three chitosan-supported ureas containing electron-withdrawing groups. These catalysts were characterized and employed as organocatalysts in different transformations, including the enantioselective cyanosilylation of α-ketoesters and aldehydes, the asymmetric addition of formaldehyde tert-butyl hydrazone to prochiral α-ketoesters and a Friedel-Crafts reaction. Several parameters that can affect the activity and selectivity of the reactions w… Show more

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Cited by 13 publications
(6 citation statements)
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“…Once tacrine derivatives were obtained, they were linked to the biopolymer through amino group of chitosan obtaining different bridges between chitosan and tacrine, in the same way that other types of chitosan derivatives have been obtained by our research group. 6,7 Starting polymeric material was characterized to obtain the degree of deacetylation (DD = 84%) and molecular weight (Mw = 87875 g· mol -1 ). Both parameters are the essential fingerprint for polymers characterization.…”
Section: Scheme 2 Synthesis Of Tacrine Derivatives By Methodology Bmentioning
confidence: 99%
“…Once tacrine derivatives were obtained, they were linked to the biopolymer through amino group of chitosan obtaining different bridges between chitosan and tacrine, in the same way that other types of chitosan derivatives have been obtained by our research group. 6,7 Starting polymeric material was characterized to obtain the degree of deacetylation (DD = 84%) and molecular weight (Mw = 87875 g· mol -1 ). Both parameters are the essential fingerprint for polymers characterization.…”
Section: Scheme 2 Synthesis Of Tacrine Derivatives By Methodology Bmentioning
confidence: 99%
“…Recently, de Gonzalo et al. reported the synthesis of three chitosan‐supported ureas bearing EWGs, and documented their application as heterogeneous hydrogen‐bonding promotors in asymmetric C−C bond‐formation reactions (Scheme ) . The effect of different parameters, such as temperature, solvents, and catalyst loading, on the catalytic activity and stereoselectivity was evaluated in three C−C bond‐forming reactions: 1) the enantioselective cyanosilylation of α‐ketoesters and aldehydes, 2) the addition of formaldehyde tert ‐butylhydrazone ( 25 ) to ethyl benzoylformate ( 24 ), and 3) the Friedel–Crafts alkylation of indole ( 26 ) by trans ‐β‐nitrostyrene ( 27 ).…”
Section: Natural Polysaccharide‐based Organocatalystsmentioning
confidence: 99%
“…Recently,d eG onzalo et al reported the synthesis of three chitosan-supported ureas bearingE WGs, and documented their application as heterogeneous hydrogen-bonding promotors in asymmetric CÀCb ond-formation reactions (Scheme 19). [62] The effect of differentp arameters, such as temperature, solvents, and catalystloading, on the catalytic activity and stereoselectivity was evaluated in three CÀCb ond-forming reactions:1 )the enantioselective cyanosilylationo fa-ketoesters and aldehydes,2 )the addition of formaldehyde tert-butylhydrazone (25)t oe thyl benzoylformate (24), and 3) the Friedel-Crafts alkylation of indole (26)b ytrans-b-nitrostyrene (27). Medium-and low-molecular-weight chitosan, with 81 and 84 % DDA, respectively,w ere used fort he synthesis of the catalysts, and N-substitution degrees ranging from 0.02 to 0.14 were cal-culated by meanso f 1 HNMR spectroscopy.T he structure of the best performing urea, 23,i sr eported in Scheme19.…”
Section: Chitosan-supported Organocatalystsmentioning
confidence: 99%
“…A set of chitosan‐supported ureas have been recently synthesized and employed in different selective procedures, including the cyanosilylation of aldehydes and activated ketones, the addition of formaldehyde tert ‐butyl hydrazone to α‐ketoesters and the Friedel‐Crafts reaction between indole and trans ‐ 2 a . The selectivities obtained for all the reactions are low, but the catalysts showed a good activity and a high stability, as they can be reused for more than 11 cycles without loss in their properties.…”
Section: Catalyst Immobilization Onto Polymeric Materials Via Post Momentioning
confidence: 99%