Two new type of 1,3,2-oxazaborolidines were prepared from (Is,2s)-2-amino-1-(4-nitrophenyl)-propane-1-3-diol and were used as catalyst in the asymmetric reduction of acetophenone. The influence of the reaction tempera...Two new type of 1,3,2-oxazaborolidines were prepared from (Is,2s)-2-amino-1-(4-nitrophenyl)-propane-1-3-diol and were used as catalyst in the asymmetric reduction of acetophenone. The influence of the reaction temperature as well as the effect of the structure of catalyst on the enantioselectivity was investigated. The origin of the products' configuration was discussed.展开更多
Two new chiral oxazaborolidine derivated from L-cystine have been used to catalyze the enantioselective reduction of prochiral ketones and the secondary alcohols are obtained with good to excellent opitical yields.
The enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine is discussed by the density functional theory (DFT) method. The main intermediates and transition states for this reaction ar...The enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine is discussed by the density functional theory (DFT) method. The main intermediates and transition states for this reaction are optimized completely at the B3LYP/6-31g(d) level, and the transition states are verified by vibrational modes. As shown, the chirality-controlled steps for this re- action are the hydride transfer from borane to carbonyl carbon and oxime carbon of keto oxime ether, and the chirality for the reduced products is determined in these two reaction steps. In all examined reaction paths, the first hydride is transferred via a six-membered ring and the second hydride via a five-membered ring or a four-membered ring.展开更多
Theab initio molecular orbital study on the mechanism of enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine is performed. As illustrated, this enantioselective reduct...Theab initio molecular orbital study on the mechanism of enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine is performed. As illustrated, this enantioselective reduction is exothermic and goes mainly through the formations of the catalyst-borane adduct, the catalyst-borane-3,3-dimethyl butanone-2 adduct, and the catalyst-alkoxyborane adduct with a B-O-B-N 4-member ring and through the decomposition of the catalyst-alkoxyborane adduct with the regeneration of the catalyst. During the hydride transfer in the catalyst-borane-3,3-dimethyl butanone-2 adduct to form the catalyst-alkoxyborane adduct, the hydride transfer and the formation of the B-O-B-N 4-member ring in the catalyst-alkoxyborane adduct happen simultaneously. The controlling step for the reduction is the transfer of hydride from the borane moiety to the carbonyl carbon of 3,3-dimethyl butanone-2. The transition state for the hydride transfer is a twisted chair structure and the reduction leads to R-chiral alcohols.展开更多
A series of alkyl 4-dialkylaminophenyl ketones were prepared and reduced asymmetrically by borane under the chiral oxazaborolidine catalysis. The results indicate that the ketones show a more obvious subsfituent effec...A series of alkyl 4-dialkylaminophenyl ketones were prepared and reduced asymmetrically by borane under the chiral oxazaborolidine catalysis. The results indicate that the ketones show a more obvious subsfituent effect on the enanfioselectivity than the corresponding 4-alkyl/alkoxy/alkylthiophenyl ketones in the asymmetric reduction because of the existence of a strong coordinate nitrogen atom with the boron atom in the catalyst and borane.展开更多
基金This work was supported by, the NNSFC.!(29972012)
文摘Two new type of 1,3,2-oxazaborolidines were prepared from (Is,2s)-2-amino-1-(4-nitrophenyl)-propane-1-3-diol and were used as catalyst in the asymmetric reduction of acetophenone. The influence of the reaction temperature as well as the effect of the structure of catalyst on the enantioselectivity was investigated. The origin of the products' configuration was discussed.
文摘Two new chiral oxazaborolidine derivated from L-cystine have been used to catalyze the enantioselective reduction of prochiral ketones and the secondary alcohols are obtained with good to excellent opitical yields.
文摘The enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine is discussed by the density functional theory (DFT) method. The main intermediates and transition states for this reaction are optimized completely at the B3LYP/6-31g(d) level, and the transition states are verified by vibrational modes. As shown, the chirality-controlled steps for this re- action are the hydride transfer from borane to carbonyl carbon and oxime carbon of keto oxime ether, and the chirality for the reduced products is determined in these two reaction steps. In all examined reaction paths, the first hydride is transferred via a six-membered ring and the second hydride via a five-membered ring or a four-membered ring.
基金the Key Project of Science and Technology of the Ministry of Education, China.
文摘Theab initio molecular orbital study on the mechanism of enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine is performed. As illustrated, this enantioselective reduction is exothermic and goes mainly through the formations of the catalyst-borane adduct, the catalyst-borane-3,3-dimethyl butanone-2 adduct, and the catalyst-alkoxyborane adduct with a B-O-B-N 4-member ring and through the decomposition of the catalyst-alkoxyborane adduct with the regeneration of the catalyst. During the hydride transfer in the catalyst-borane-3,3-dimethyl butanone-2 adduct to form the catalyst-alkoxyborane adduct, the hydride transfer and the formation of the B-O-B-N 4-member ring in the catalyst-alkoxyborane adduct happen simultaneously. The controlling step for the reduction is the transfer of hydride from the borane moiety to the carbonyl carbon of 3,3-dimethyl butanone-2. The transition state for the hydride transfer is a twisted chair structure and the reduction leads to R-chiral alcohols.
基金Project supported partly by the National Natural Science Foundation of China （Nos. 20272002 and 20472005） and the Excellent Young Teacher Program and the Scientific Research Foundation for the Returned 0versea Chinese Scholars of Ministry of Education of China.
文摘A series of alkyl 4-dialkylaminophenyl ketones were prepared and reduced asymmetrically by borane under the chiral oxazaborolidine catalysis. The results indicate that the ketones show a more obvious subsfituent effect on the enanfioselectivity than the corresponding 4-alkyl/alkoxy/alkylthiophenyl ketones in the asymmetric reduction because of the existence of a strong coordinate nitrogen atom with the boron atom in the catalyst and borane.
