Lithium bromide as a new catalyst for carbon–carbon bond formation in the solid state

Iodine a Simple, Effective and Inexpensive Catalyst for the Synthesis of Substituted Coumarins

“…Interestingly, the Knoevenagel condensation of o-hydroxybenzaldehyde with ethyl acetoacetate was also found to proceed effectively in the presence of iodine under microwave irradiations in the molten state and the corresponding coumarin derivative was obtained in 80% yield (Scheme 2). In an earlier report we employed LiBr efficiently in the Knoevenagel condensation of salicylaldehyde with active methylene compounds for the synthesis of coumarin derivatives [32]. However, the von Pechmann condensation using LiBr under microwave irradiation without using any solvent did not proceed as efficiently as it proceeds with molecular iodine, and the corresponding coumarin derivatives were obtained in 30-50% yields.…”

Evaluation of the nitroaldol reaction in the presence of metal ion-crosslinked alginates

“…Among the numerous reports dealing with metal-catalyzed 43 and organocatalyzed-Henry reactions, 44 the solid-state condensation of carbonyl compounds with active methylene compounds in the presence of lithium bromide as a mild Lewis acid catalyst has also been described. 45 Taking everything into consideration, as well as the fact that calcium is one of the cheapest commercially available metals, the fifth most-abundant element in earth's crust, and non-toxic, 46,47 we decided to investigate the ability of Ca 2+ -containing alginate biohydrogels to promote the Henry reaction. In preliminary experiments using the model reaction between 4-nitrobenzaldehyde (1a) and nitromethane (2a), we were delighted to observe the gradual formation of the desired b-nitroalcohol 3a in the presence of Ca 2+ -AHG beads under mild conditions (DMSO, room temperature).…”

Simple Protocol for the Knoevenagel Condensation Under Solvent Free Conditions using Tungstophosphoric Acid as Catalyst

“…Knoevenagel condensation is one of the most important organic reactions [1]. The reaction is generally performed between condensation of active methylene and carbonyl compounds in presence of some basic [2,3] or Lewis acid catalyst [4][5][6][7][8]. The Knoevenagel condensation products are further used in various organic reactions such as Michael additions and Diels-Alder reactions [9].…”