Indium(III)-Catalyzed Knoevenagel Condensation of Aldehydes and Activated Methylenes Using Acetic Anhydride as a Promoter

Abstract

The combination of a catalytic amount of InCl3 and acetic anhydride remarkably promotes the Knoevenagel condensation of a variety of aldehydes and activated methylene compounds. This catalytic system accommodates aromatic aldehydes containing a variety of electron-donating and -withdrawing groups, heteroaromatic aldehydes, conjugate aldehydes, and aliphatic aldehydes. Central to successfully driving the condensation series is the formation of a geminal diacetate intermediate, which was generated in situ from an aldehyde and an acid anhydride with the assistance of an indium catalyst.

The green Knoevenagel condensation: solvent-free condensation of benzaldehydes

“…Alternatively, Knoevenagel protocols have been developed that use Lewis acids such as LiOH, ZnCl 2 , InCl 3 , TiCl 4 , and NbCl 5 (20)(21)(22) and various heterogeneous solid bases as a catalyst (23). However, the use of heavy metals for the synthesis of food and pharmaceutical products is not desirable because of their toxicity (24).…”

Enzyme Promiscuity as a Remedy for the Common Problems with Knoevenagel Condensation

“…Recently, Ogiwara et al. have shown that an acetic anhydride used together with indium(III)‐catalyst acts as a promoter of the Knoevenagel reaction . The driving force of the presented method was 1,1‐diacetate, which was generated in situ from an aldehyde.…”

“…[20] Althought he additiono ft he acetic anhydride to the reaction medium subtly affects the yield of the target product 3a (Table 2, entry 10), its presence completely suppresses formation of undesired bis-adduct 4.R ecently,O giwara et al have shown that an acetic anhydride used together with indium(III)catalysta cts as ap romoter of the Knoevenagel reaction. [29] The driving force of the presented method was 1,1-diacetate, which was generated in situ from an aldehyde. Under the studied reaction conditions with acetic anhydride we did not observe the formation of such an intermediate.…”

Cellulose stabilized Fe3O4and carboxylate‐imidazole and Co‐based MOF growth as an exceptional catalyst for the Knoevenagel reaction

“…[46] Various catalysts including Lewis acids, zeolites, and different amines have been utilized to catalyze the Knoevenagel reaction. [47][48][49] Recently, the various solidsupported heterogeneous catalysts have been applied to Knoevenagel reaction including Hf (IV) MOF, [50] metalcoordinated, resorcin [4]arene-based molecular trimer, [51] GO-supported PdNi nanoparticles, [52] Zn-based MOF, [53] amino-functionalized Zn/Cd-MOFs, [54] Cu (II)-based metal-organic macrocycle and framework, [55] covalent organic frameworks (COFs) [56] and Core-Shell MOF/ COF. [57] In the present work, Fe 3 O 4 /cellulose/Co-MOF was hydrothermally prepared and utilized as an efficient and cost-effective heterogeneous catalyst for the Knoevenagel reaction under solvent-free conditions.…”