A novel magnetically recoverable thioporphyrazine catalyst（CoPz（S-Bu）8/SiO2@Fe3O4） was prepared by immobilization of the cobalt octkis（butylthio） porphyrazine complex（CoPz（S-Bu）8） on silica-coated magnetic n...A novel magnetically recoverable thioporphyrazine catalyst（CoPz（S-Bu）8/SiO2@Fe3O4） was prepared by immobilization of the cobalt octkis（butylthio） porphyrazine complex（CoPz（S-Bu）8） on silica-coated magnetic nanospheres（SiO2@Fe3O4）. The composite CoPz（S-Bu）8/SiO2@Fe3O4appeared to be an active catalyst in the oxidation of benzyl alcohol in aqueous solution using hydrogen peroxide（H2O2） as oxidant under Xe-lamp irradiation,with 36.4% conversion of benzyl alcohol, about 99% selectivity for benzoic acid and turnover number（TON） of 61.7 at ambient temperature. The biomimetic catalyst CoPz（S-Bu）8was supported on the magnetic carrier SiO2@Fe3O4 so as to suspend it in aqueous solution to react with substrates, utilizing its lipophilicity. Meanwhile the CoPz（S-Bu）8can use its unique advantages to control the selectivity of photocatalytic oxidation without the substrate being subjected to deep oxidation. The influence of various reaction parameters on the conversion rate of benzyl alcohol and selectivity of benzoic acid was investigated in detail. Moreover, photocatalytic oxidation of substituted benzyl alcohols was obtained with high conversion and excellent selectivity, specifically conversion close to 70%, selectivity close to 100% and TON of 113.6 for para-position electron-donating groups. The selectivity and eco-friendliness of the biomimetic photocatalyst give it great potential for practical applications.展开更多
Transition-metal-catalyzed asymmetric benzylic substitution of racemic benzyl esters is an efficient and straightforward route towards the construction of benzylic stereocenters but remains a challenge,due to the diff...Transition-metal-catalyzed asymmetric benzylic substitution of racemic benzyl esters is an efficient and straightforward route towards the construction of benzylic stereocenters but remains a challenge,due to the difficulty encountered in the suppression ofβ–H elimination and asymmetric induction.Herein,we successfully developed a highly diastereo-and enantioselective benzylic substitution of racemic 1-(aryl)alkyl esters with aldimine esters enabled by Pd/Cu dual catalysis.An array of enantioenrichedα-benzyl substitutedα-amino acids containing vicinal stereocenters were prepared with high levels of diastereo-and enantioselectivities(up to>20:1 dr and>99%ee)and the practicability of the products was further illustrated via their diverse transformations.The dynamic kinetic asymmetric transformation process of the racemic benzyl esters was investigated experimentally and by computational studies.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 21272281 and 20977115)Natural Science Foundation of Hubei Province (2014CFB919)+1 种基金"the Fundamental Research Funds for the Central Universities", South-Central University for Nationalities (CZY14003)the Science and Technology Plan Innovation Team of Wuhan City (2015070504020220)
文摘A novel magnetically recoverable thioporphyrazine catalyst（CoPz（S-Bu）8/SiO2@Fe3O4） was prepared by immobilization of the cobalt octkis（butylthio） porphyrazine complex（CoPz（S-Bu）8） on silica-coated magnetic nanospheres（SiO2@Fe3O4）. The composite CoPz（S-Bu）8/SiO2@Fe3O4appeared to be an active catalyst in the oxidation of benzyl alcohol in aqueous solution using hydrogen peroxide（H2O2） as oxidant under Xe-lamp irradiation,with 36.4% conversion of benzyl alcohol, about 99% selectivity for benzoic acid and turnover number（TON） of 61.7 at ambient temperature. The biomimetic catalyst CoPz（S-Bu）8was supported on the magnetic carrier SiO2@Fe3O4 so as to suspend it in aqueous solution to react with substrates, utilizing its lipophilicity. Meanwhile the CoPz（S-Bu）8can use its unique advantages to control the selectivity of photocatalytic oxidation without the substrate being subjected to deep oxidation. The influence of various reaction parameters on the conversion rate of benzyl alcohol and selectivity of benzoic acid was investigated in detail. Moreover, photocatalytic oxidation of substituted benzyl alcohols was obtained with high conversion and excellent selectivity, specifically conversion close to 70%, selectivity close to 100% and TON of 113.6 for para-position electron-donating groups. The selectivity and eco-friendliness of the biomimetic photocatalyst give it great potential for practical applications.
基金supported by the National Key R&D Program of China(grant no.2023YFA1506700)the National Natural Science Foundation of China(NSFC,grant nos.21831005,21991112,and 22171183).
文摘Transition-metal-catalyzed asymmetric benzylic substitution of racemic benzyl esters is an efficient and straightforward route towards the construction of benzylic stereocenters but remains a challenge,due to the difficulty encountered in the suppression ofβ–H elimination and asymmetric induction.Herein,we successfully developed a highly diastereo-and enantioselective benzylic substitution of racemic 1-(aryl)alkyl esters with aldimine esters enabled by Pd/Cu dual catalysis.An array of enantioenrichedα-benzyl substitutedα-amino acids containing vicinal stereocenters were prepared with high levels of diastereo-and enantioselectivities(up to>20:1 dr and>99%ee)and the practicability of the products was further illustrated via their diverse transformations.The dynamic kinetic asymmetric transformation process of the racemic benzyl esters was investigated experimentally and by computational studies.
