- A convergent approach for the total synthesis of the α-glucosidase inhibitor (-)-panaxjapyne-C
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The stereoselective total synthesis of (-)-panaxjapyne-C was accomplished in a convergent fashion. The synthesis utilizes the readily available enantiomers l-(+)-diethyltartrate and d-(-)-diethyltartrate and involves a Cadiot-Chodkiewicz coupling reaction, and an Ohira-Bestmann reaction as the key steps.
- Sathish Reddy,Gangadhar,Srihari
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p. 1524 - 1530
(2013/12/04)
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- Carbene-metal hydrides can be much less acidic than phosphine-metal hydrides: Significance in hydrogenations
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Acidities of iridium hydride intermediates were shown to be critical in some transformations mediated by the chiral analogues of Crabtree's catalyst, 1-3. To do this, several experiments were undertaken to investigate the acidities of hydrogenation mixtures formed using these iridium-oxazoline complexes. DFT calculations indicated that the acidity difference for Ir-H intermediates in these hydrogenations were astounding; iridium hydride from the N-heterocyclic carbene catalyst 1 was calculated to be around seven pK a units less acidic than those from the P-based complexes 2 and 3. Consistent with this, the carbene complex 1 was shown to be more effective for hydrogenations of acid-sensitive substrates. In deuteration experiments, less "abnormal" deuteration was observed, corresponding to fewer complications from acid-mediated alkene isomerization preceding the D 2-addition step. Finally, simple tests with pH indicators provided visual evidence that phosphine-based catalyst precursors give significantly more acidic reaction mixtures than the corresponding N-heterocyclic carbene ones. These observations indicate carbene-for-phosphine (and similar) ligand substitutions may impact the outcome of catalytic reactions by modifying the acidities of the metal hydrides formed.
- Zhu, Ye,Fan, Yubo,Burgess, Kevin
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supporting information; experimental part
p. 6249 - 6253
(2010/06/20)
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- A Concise and Enantioselective Approach to Cyclobutanones by Tandem Asymmetric Epoxidation and Enantiospecific Ring Expansion of Cyclopropylidene Alcohols. An Enantiocontrolled Synthesis of (+)- and (-)-α-Cuparenones
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A tandem Katsuki-Sharpless asymmetric epoxidation and enantiospecific ring expansion of 2-alkyl(or 2-aryl)-2-cyclopropylideneethanols (1a-i) afforded chiral 1-alkyl(or 1-aryl)-1-(hydroxymethyl)cyclobutanones (3a-i) in high yields and high enantiomeric excess.These compounds are potentially valuable synthons for the enantioselective creation of the quaternary carbons.Hence, this enabled us to accomplish a concise and enantioselective total synthesis of both (+)- and (-)-cuparenones (11).
- Nemoto, Hideo,Ishibashi, Hiroki,Nagamochi, Masatoshi,Fukumoto, Keiichiro
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p. 1707 - 1712
(2007/10/02)
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- THE REACTION OF O-SILYLATED α-KETOLS WITH TRIMETHYLSILYL CYANIDE
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The reactions of a series of O-silylated α-ketols with trimethylsilyl cyanide have been investigated.Formation of the expected O-trimethylsilyl cyanohydrins as major products has been shown to be accompanied by the hitherto unsuspected formation of a disi
- Still, Ian W. J.,Daoquan, Wang
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