Organocatalytic Knoevenagel Condensations by Means of Carbamic Acid Ammonium Salts

Abstract

The Knoevenagel condensation between an active methylene compound and an aromatic aldehyde with a carbamic acid ammonium salt used as an organocatalyst gave the desired Knoevenagel products in up to 98% yield. The reaction occurred at rt and in a short reaction time under solvent-free conditions. In addition, no extraction, wash, or chromatography steps were needed to obtain a high-purity Knoevenagel product.

A novel synthesis of stable 3H-pyrrolizine fused diazaborepin

“…Subsequent elimination of piperidine step by step from d to e and cyclization to afford pyrrolizine f from the Mannich type d and e is facile and gives the condensation product NDAB after isomerization. 27 NMR spectroscopic data for NDAB and DAB are consistent with their structure information. As shown in Figure 2, the hydrogen bond proton of the naked diazaborepin ring NDAB appears as a singlet at 15.77 ppm, while it disappears for DAB after coordination with BF 3 ÁOEt 2 .…”

“…22 The route developed is shown in Scheme 1 and relies on an organocatalyst (piperidinium acetate) which formed from the reaction of piperidine and glacial acetic acid in situ and had been used in Knoevenagel reaction extensively. [27][28][29][30] The detailed preparation procedures were exhibited in SI. In the first step, 2,3,3-trimethylindole 3 reacted with 2-formylpyrrole 4 under organocatalyst.…”

The green Knoevenagel condensation: solvent-free condensation of benzaldehydes

“…Often, microwave reactions are used, but these also have their limitations on scalability, applicability, and energy use (25)(26)(27)(28). The present work, therefore, explores the possibilities to conduct the Knoevenagel reaction of syringaldehyde and malonic acid without pyridine and piperidine using a solventfree condensation which employs environmentally benign amines and ammonium salts as catalysts (29). After the reaction has been optimized for syringaldehyde, the scope of the method will be explored using various benzaldehydes with different electron-donating or electron-withdrawing groups, see Figure 1.…”

First report of the application of simple molecular complexes as organo-catalysts for Knoevenagel condensation

“…1 The useful synthetic techniques is expected to contain one-pot 25 single step using environmentally benign non-hazardous catalyst and solvent-free condition. 2 Performing an organic reaction in environmentally suitable mode is still a challenge to the chemist even today.…”

“…24 Further Mase et.al. have also reported eco-friendly organo-catalysed 10 Knoevenagel condensation but preparation, stability and recyclability of organo-catalyst are still challenging factors. 25 In our continuation of work with various kind of molecular complexes, we are reporting for the first time the use of simple molecular complexes (chart 1) based on weak acid and tertiary 15 amine as organo-catalyst for the popular Knoevenagel condensation reaction. The mechanistic aspects of Knoevenagel condensation using these molecular complexes has been investigated and presented in our present work.…”