Recent Applications of Niobium Catalysts in Organic Synthesis

Abstract

Niobium catalysts generally possess a good Lewis acidity and have received increased attention in recent years. The applications of niobium pentachloride as Lewis acid in organic synthesis have been recently reviewed. Since then, there has been an increasing number of examples on the use of niobium catalysts in organic reactions such as Biginelli reactions, Friedel-Crafts acylation and Sakurai-Hosomi reactions of acetals, Knoevenagel condensation, acetylation of alcohols and phenols, among others. Also, chiral niobium complexes have been reported to give high enantiomeric excesses in asymmetric Mannich-type reactions.In this review, recent applications of these versatile reagents in organic synthesis, including our own results, will be disclosed.

NbCl5-catalyzed sulfa-Michael addition for constructing quaternary centers in enones

“…Based on the previous catalysis using NbCl 5 , 7 we proposed a plausible mechanism in Scheme 6. We reckon that the reaction is initiated by the formation of niobium species 4 between NbCl 5 and thiol 2 .…”

Efficient one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives promoted by niobium pentachloride

“…NbCl 5 forms chloro-bridged dimers in its solid state in which each niobium atom is surrounded by a distorted octahedron of chlorine atoms. NbCl 5 is highly electrophilic and can act as a Lewis acid, promoting several organic transformations (Batista et al, 1997;Kobayashi et al, 2000;Constantino et al, 2001Constantino et al, , 2004Constantino et al, , 2005Constantino et al, , 2007Andrade, 2004;da Silva-Filho et al, 2005Andrade & Rocha, 2006;Wang et al, 2007;Polo et al, 2008;Cai et al, 2010;Hou et al, 2010Hou et al, , 2011Lacerda et al, 2012;Liu et al, 2013;Martins et al, 2013;dos Santos et al, 2013;Bian et al, 2014;Nasseri et al, 2014).…”

Development of Trifluoromethanesulfonic Acid-Immobilized Nitrogen-Doped Carbon-Incarcerated Niobia Nanoparticle Catalysts for Friedel–Crafts Acylation

“…To obtain more active catalysts, we found that TfOH-treated nitrogen-doped carbon-incarcerated niobia NP catalysts (NCI-Nb-TfOH) showed high activity in Friedel–Crafts acylation with lower loading of catalysts. In general, niobium catalysts possess a high Lewis acidity and have been investigated in many organic syntheses for this reason . Possessing both strong Lewis and strong Brønsted acidic sites, Nb 2 O 5 and its hydrate have played important roles in the construction of heterogeneous catalysts and in acid-catalyzed reactions .…”