Chitosan as heterogeneous catalyst in Michael additions: The reaction of cinnamonitriles with active methyls, active methylenes and phenols

Abstract

The reaction of active methylene moieties, pyrazolones, thiazolylacetonitriles, phenols and alkyl pyridazinones with benzylidene-malononitrile in ethanol in presence of chitosan afforded aminopyrancarbonitriles, pyranopyrazole, thiazolopyridines, chromenes, and pthalazines in yields comparable to those obtained in ethanolic piperidine. Much lower yields were obtained in aqueous solutions.

Chitosan as a Sustainable Organocatalyst: A Concise Overview

“…[138] Comparable results were also observed by Diaz et al, who used a hydrogel biopolymer as the catalyst during the condensation of benzylidenemalonitrile to cyclohexanone or recorcinol in water at reflux. [99] Recently, Khalil et al grafted poly(vinylpyridine) onto the chitosan backbone under heterogeneous conditions.…”

“…Michael-type addition of benzylidenemalonitrile to geminal dicyanoalcenes, 2-phenyl-1-propene-1,1-dicarbonitrile and 2amino-1-propene-1,1,3-tricarbonitrile, in ethanol provides the resulting cyclic compounds in 43 and 63 % yield, respectively (Scheme 16). [138] Comparable results were also observed by Diaz et al, who used a hydrogel biopolymer as the catalyst during the condensation of benzylidenemalonitrile to cyclohexanone or recorcinol in water at reflux. [99] Recently, Khalil et al grafted poly(vinylpyridine) onto the chitosan backbone under heterogeneous conditions.…”

“…In this direction, Al-Matar et al recently reported the use of chitosan as a catalyst in Michael-type additions. [138] Although no indications were provided about the chitosan catalyst used (deacetylation degree, molecular weight, preparation method, amount of catalyst with respect to the reactants, and amount of accessible amine groups on the surface), the catalyst seems to operate efficiently (Scheme 14). Indeed, benzylidenemalonitrile reacts with ethylacetoacetate in ethanol in the presence of chitosan to afford the desired cyclic aminopyranecarbonitrile compound in 59 % yield (Scheme 14).…”

“…Michael addition of benzylidenemalonitrile to geminal dicyanoalcenes catalyzed by chitosan. [138] Scheme 17. Preparation of the CS-Pyr catalyst.…”

Chitosan-MgO Nanocomposite: One Pot Preparation and Its Utility as an Ecofriendly Biocatalyst in the Synthesis of Thiazoles and [1,3,4]thiadiazoles

“…Although this biopolymer has many advantages, such as its renewability, biocompatibility, and biodegradability, its utility is limited in its unmodified form. For a long time, chitosan was used as an ecofriendly basic catalyst in some organic reactions [4,5,6,7]. However, the major problem of its use is the limited basic properties (weak catalytic activity) and its high swelling properties and gel formation renders its separation and recovery very difficult.…”