“…However, the poor reactivity of “chiral cyclohexyl short arms” has become an indication of the level of steric incumbrance that can be tolerated in a reactive homochiral porphyrin complex. Compressing the size of the ring, e.g., choosing cyclopentane, cyclobutane, and cyclopropane rings, could be a good alternative to overcome this hurdle, as reported previously with chiral phosphines in the asymmetric hydrogenation. − …”
Section: 22 Ruthenium Porphyrinsmentioning
confidence: 96%
“…Compressing the size of the ring, e.g., choosing cyclopentane, cyclobutane, and cyclopropane rings, could be a good alternative to overcome this hurdle, as reported previously with chiral phosphines in the asymmetric hydrogenation. [157][158][159]…”
“…However, the poor reactivity of “chiral cyclohexyl short arms” has become an indication of the level of steric incumbrance that can be tolerated in a reactive homochiral porphyrin complex. Compressing the size of the ring, e.g., choosing cyclopentane, cyclobutane, and cyclopropane rings, could be a good alternative to overcome this hurdle, as reported previously with chiral phosphines in the asymmetric hydrogenation. − …”
Section: 22 Ruthenium Porphyrinsmentioning
confidence: 96%
“…Compressing the size of the ring, e.g., choosing cyclopentane, cyclobutane, and cyclopropane rings, could be a good alternative to overcome this hurdle, as reported previously with chiral phosphines in the asymmetric hydrogenation. [157][158][159]…”
“…Accordingly, this has led to numerous synthetic methods for constructing this aromatic heterocycle and the continued pursuit of ever more efficient and flexible approaches . Many procedures have been developed for the construction of 4‐ylidene‐5(4 H )‐oxazolone derivatives, but none of these have been extended to be general . However, some of these procedures often utilize costly reagents and afford products in only moderate yields.…”
in Wiley Online Library (wileyonlinelibrary.com).Simple, effective, and high yield synthetic procedure for the synthesis of 4-ylidene-5(4H)-oxazolones 2a-m from arylidene-malononitriles under solvent-free conditions is described. The scope of this reaction was investigated, and it was found that the presence of anhydrous sodium acetate gave the corresponding oxazolones in excellent yields. The newly generated oxazolone derivative 2m underwent ring transformation into pyrroles, imidazoles, pyridazine, and triazines.
“…As part of a broad study [1][2][3] on the structure and reactivity of dehydroamino acid derivatives as substrates for asymmetric hydrogenation catalyzed by chiral diphosphine/rhodium(I) complexes, Z-methyl 2-formamido-3-alkylacrylate esters (1) [4,5] were reduced with an in situ formed chlororhodium(I)-(-)-(1R, 2R)- (2) 277 catalyst [6,7]. Changing the steric character of the 3-substituent resulted in a very significant change in the enantiomeric excess (e.e.)…”
Hydrogenation of Z-(-)-(I'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by Pd/C was performed at atmospheric pressure to yield a mixture of (2R, I'R, 3'R, 4'S)-and (2S, I'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluorobutanoate diastereomers in a 55:45 ratio, respectively. Repeated fractional crystallization from ethyl acetate and vapor diffusion of petroleum ether afforded (+)-(2S, 1 'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluorobutanoate as clear colorless, crystalline prisms which were subjected to single-crystal X-ray diffraction analysis. The crystals belong to the orthorhombic system P21212 I, and at 213 K: a = 5.054 (1) The finding of the (2S)-configuration for the formamido-acid portion of the (+)-ester enabled the configurational assignment of the asymmetric hydrogenation products of Z-methyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by chiral diphosphine/rhodium(I) complexes.
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