Highly efficient synthesis of α-aminophosphonates catalyzed by hafnium(IV) chloride

Hf(OTf)4 as a Highly Potent Catalyst for the Synthesis of Mannich Bases under Solvent-Free Conditions

“…Compared to the reaction in acetonitrile, the one performed in EtOH resulted in shorter reaction time and higher yield (94% yield, 5 h). But when the reaction in EtOH was elevated to 80 °C, to our surprise, the reaction rate and yield of Hf(OTf)4-catalyzed Mannich reaction was not significantly affected like many other reactions [42][43][44]. Hf(OTf) 4 6 89 a Benzaldehyde/aniline/acetophenone are in a 1:1:2 molar ratio.…”

“…Our ongoing research in this field showed that Hf(IV) salts are even more potent than Zr(IV) salts in many carbonyl-transformation Previous research on Group IVB transition metal (Zr(IV) and Hf(IV)) catalysts revealed their superior activity on many carbonyl-transformation reactions [30,43]. Our ongoing research in this field showed that Hf(IV) salts are even more potent than Zr(IV) salts in many carbonyltransformation reactions [44][45][46]. However, the catalytic effect of Hf(IV) salts on Mannich reaction has never been explored.…”

“…Hf(OTf) 4 -catalyzed Mannich reaction exhibited excellent regioselectivity and diastereoselectivity when alkyl ketones were employed as substrates. 1 H NMR tracing of the H/D exchange reaction of ketones in MeOH-d 4 indicated that Hf(OTf) 4 could significantly promote the keto-enol tautomerization, thereby contributing to the acceleration of reaction rate.Molecules 2020, 25, 388 2 of 11 reactions [44][45][46]. However, the catalytic effect of Hf(IV) salts on Mannich reaction has never been explored.…”

“…Molecules 2020, 25, 388 2 of 11 reactions [44][45][46]. However, the catalytic effect of Hf(IV) salts on Mannich reaction has never been explored.…”

Activated Carbon Supported Hafnium(IV) Chloride as an Efficient, Recyclable, and Facile Removable Catalyst for Expeditious Parallel Synthesis of Benzimidazoles

“…Yin and Gao also reported that the metallocenes of Ti(IV) [16] and Zr(IV) [17] were highly efficient Lewis acids for other carbonyl-transformation reactions. In recent years, HfCl 4 , another closely related Group IVB transition metal salt, was revealed to possess even superior activities in many metal Lewis acid-catalyzed reactions [18][19][20], especially those involving carbonyl activation [21][22][23][24]. In addition, it is noteworthy that ZrOCl 2 ·8H 2 O, ZrCl 4 , and HfCl 4 showed high catalytic activity in the synthesis of 2-substituted benzimidazoles from o-phenylenediamines and orthoesters [25].…”