epoxides to obtain cyclic carbonates in high yields under operationally simple atmospheric pressure conditions. Additional DFT calculations substantiate a mechanism involving an initial addition of the nucleophiliciodide counter anion of the ammonium salt to the H-bonding activated epoxide, followed by stepwise CO2-fixation and cyclization. Graphical abstract
Thiourea-catalyzed aminolysis of N-acyl homoserine lactones
作者:Michael A. Bertucci、Stephen J. Lee、Michel R. Gagné
DOI:10.1039/c3cc00268c
日期:——
Thiourea catalysts accelerate aminolysis of N-acyl homoserine lactones (AHLs), molecules integral to bacterial quorum sensing. The catalysts afford rate enhancement of up to 10 times the control in CD3CN. Mild catalysis in other polar aprotic solvents is still observed, while the activity is attenuated in polar protic solvents.
Detailed investigations concerning the organocatalytic (asymmetric) α-azidation of prochiral β-ketoesters were carried out. It was shown that the racemic version of such a reaction can either be carried out under oxidative conditions using TMSN₃ as the azide-source with quaternary ammonium iodides as the catalysts, or by using hypervalent iodine-based electrophilic azide-transfer reagents with different
Thiourea/Proline Derivative-Catalyzed Synthesis of Tetrahydrofuran Derivatives: A Mechanistic View
作者:Suzanne M. Opalka、Jeremy L. Steinbacher、Brandon A. Lambiris、D. Tyler McQuade
DOI:10.1021/jo200838v
日期:2011.8.19
A thiourea/proline derivative-catalyzed synthesis of linear a-substituted tetrahydrofuran/pyran derivatives starting with lactol substrates is presented. This study demonstrates the utility and potential complications of using (thio)urea/proline cocatalysis as each of these catalysts is necessary to provide the observed reactivity, but a time-dependent decrease in enantioselectivity is observed. New mechanistic insights into (thio)urea/proline cocatalysis are presented.
Double Diastereocontrol in Bifunctional Thiourea Organocatalysis: Iterative Michael–Michael–Henry Sequence Regulated by the Configuration of Chiral Catalysts
The importance and reactivity consequences of the double diastereocontrol in noncovalent bifunctional organocatalysis were studied. The results suggest that the bifunctional thioureas can have synthetic limitations in multicomponent domino or autotandem catalysis. Nevertheless, we provided a means to exploit this behavior and used the configuration of the chiral catalyst as a control element in organo-sequential reactions.