N-Heterocyclic carbene-catalysed intermolecular Stetter reactions of acetaldehyde
作者:Sun Min Kim、Ming Yu Jin、Mi Jin Kim、Yan Cui、Young Sug Kim、Liqiu Zhang、Choong Eui Song、Do Hyun Ryu、Jung Woon Yang
DOI:10.1039/c0ob01178a
日期:——
A facile method for the intermolecular Stetter reaction of various Michael acceptors with acetaldehyde as a biomimetic acylanion source was realized using N-heterocyclic carbene catalysis. This catalytic system has also been applied to the enantioselective Stetter reaction and resulted in moderate to good enantioselectivities for the corresponding Stetter products.
Thiazolium-catalyzed intermolecular Stetter reaction of linear and cyclic alkyl α-diketones
作者:Olga Bortolini、Giancarlo Fantin、Marco Fogagnolo、Pier Paolo Giovannini、Alessandro Massi、Salvatore Pacifico
DOI:10.1039/c1ob06480k
日期:——
3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g.3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic
Thiazolium-functionalized polystyrene monolithic microreactors for continuous-flow umpolung catalysis
作者:Olga Bortolini、Alberto Cavazzini、Paolo Dambruoso、Pier Paolo Giovannini、Lorenzo Caciolli、Alessandro Massi、Salvatore Pacifico、Daniele Ragno
DOI:10.1039/c3gc41284a
日期:——
Thiazolium salt pre-catalysts have been immobilized on silica and monolithic polystyrene and their activity was tested under batch conditions in three model umpolung reactions, namely the benzoin condensation of benzaldehyde, the acyloin-type condensation of biacetyl, and the Stetter reaction of biacetyl with trans-chalcone. A prerequisite of the study has been the utilization of environmentally benign water and ethanol solvents. After having established the higher performance of polystyrene monolithic thiazolium carbene catalysts, their effectiveness has been tested under the flow regime by fabricating the corresponding monolithic microreactors (pressure-resistant stainless-steel columns). Importantly, it has been demonstrated by a brief substrate scope study that the polymeric matrix and the continuous flow regime synergistically contribute to preserve the activity of the carbene catalysts over time, thus permitting the long-term operation (up to 7 days) of the prepared monolithic reactors for the production of valuable compounds via the umpolung strategy.