- Non- C2-Symmetric Chiral-at-Ruthenium Catalyst for Highly Efficient Enantioselective Intramolecular C(sp3)-H Amidation
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A new class of chiral ruthenium catalysts is introduced in which ruthenium is cyclometalated by two 7-methyl-1,7-phenanthrolinium heterocycles, resulting in chelating pyridylidene remote N-heterocyclic carbene ligands (rNHCs). The overall chirality results from a stereogenic metal center featuring either a or Δabsolute configuration. This work features the importance of the relative metal-centered stereochemistry. Only the non-C2-symmetric chiral-at-ruthenium complexes display unprecedented catalytic activity for the intramolecular C(sp3)-H amidation of 1,4,2-dioxazol-5-ones to provide chiral -lactams with up to 99:1 er and catalyst loadings down to 0.005 mol % (up to 11 ?200 TON), while the C2-symmetric diastereomer favors an undesired Curtius-type rearrangement. DFT calculations elucidate the origins of the superior C-H amidation reactivity displayed by the non-C2-symmetric catalysts compared to related C2-symmetric counterparts.
- Zhou, Zijun,Chen, Shuming,Hong, Yubiao,Winterling, Erik,Tan, Yuqi,Hemming, Marcel,Harms, Klaus,Houk,Meggers, Eric
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p. 19048 - 19057
(2019/12/04)
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- [5]HELOL phosphite: A helically grooved sensor of remote chirality
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Even when the first center of chirality is far from a functional group, the stereochemistries of chiral molecules can be sensed if the functional group is attached to a phosphorus embedded within the groove of a nonracemic helicene. The sensor used was a phosphite ester of [5]HELOL, structure 6, and 31P NMR spectroscopy was the method of analysis. Although there are seven methylenes between the hydroxyl and the first center of chirality, the 31P NMRs could distinguish the enantiomers of 8-phenylnonanol with baseline resolution. However, to achieve this resolution, the solvent has to be chosen appropriately. The probe can also analyze the enantiomers of other alcohols, amines, phenols, and, when they were coupled to 2-aminophenol, carboxylic acids. The sensitivity to remote chiral centers of the moieties, analyzed is attributed to their confinement to the helical groove.
- Weix,Dreher,Katz
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p. 10027 - 10032
(2007/10/03)
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- Chemoselective rhodium-carbenoid reaction with the aromatic nucleus: An efficient methodology for 2-indanones, 2- Tetralones and 2-benzosuberones and its application in the synthesis of (±)-ar-Himachalene
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Rhodium-carbenoid species derived from rhodium acetate- catalyzed decomposition of aryl alkyl α- diazoke-tones have been shown to display a chemoselective addition into the aromatic nucleus, instead of insertion into an aliphatic C-H site. The synthetic u
- Sudrik,Nanjundiah,Sonawane
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p. 1103 - 1112
(2007/10/03)
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