- One-pot preparation of oxazol-5(4H)-ones from amino acids in aqueous solvents
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A method for one-pot synthesis of oxazol-5(4H)-ones has been developed using 4-(4,6-dimethoxy-l,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), which is available for the activation of carboxylic acids in an aqueous solvent. The oxazolones were prepared by the TV-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids by the addition of N,N-diethylaniline. Since both these reactions proceed effectively with the same coupling reagent, DMT-MM, in aqueous solvents, the procedure is simplified and becomes easy to perform. In addition, 5-(triazinyloxy)oxazole derivatives have been synthesized by controlling the basicity of the reaction system.
- Fujita, Hikaru,Kunishima, Munetaka
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p. 907 - 912
(2012/08/08)
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- A new method proposed for the determination of absolute configurations of α-amino acids
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Enantiopure α-amino acids were converted to 4-substituted 2-aryl- and 2-alkyl-5(4H)-oxazolones under partial racemization. These nonracemic mixtures were dissolved in CDCl3, an equimolar amount of the chiral dirhodium complex Rh2(II)[(R)-(+)-MTPA]4 (MTPA-H = Mosher's acid) was added, and the 1H NMR spectra of the resulting samples were recorded [dirhodium method). The relative intensities of 1H signals dispersed by the formation of diastereomeric adducts allow to determine the absolute configuration (AC) of the starting a-amino acids. Binding atoms in the adducts were identified by comparing the 1H and 13C chemical shifts of the oxazolones in the absence and presence of Rh2(II)[(R)-(+)- MTPA]4. Thereby, information about the scope and limits of this method can be extracted. A protocol how to use this method is presented. Copyright
- Gomez, Edison Diaz,Duddeck, Helmut
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experimental part
p. 222 - 227
(2010/02/28)
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- Preparation, separation of diastereoisomers, and X-ray determination of configurations of (5R)-and (5S)-5-benzoylamino-5-[(1S)-methylpropyl]-4-oxo-1,3-dioxanes
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(5R)-and (5S)-5-benzoylamino-5-[(1S)-methylpropyl]-4-oxo-1,3-dioxanes were obtained via α-hydroxymethylation of (4S)-2-phenyl-4-[(1S)-methylpropyl]-5(4H)-oxazolone derived from N-benzoyl-L-isoleucine. The isomer 5R crystallized in a space group P21 with a = 7.071(1), b = 10.998(3), c = 9.884(1) A and β = 109.58(2)°, while isomer 5S in a P212121 with a = 6.477(1), b = 10.023(1) and c = 21.901(6) A. The configurations of both diastereoisomers were established by X-ray methods. Semi-rigid conformation of the whole 5-benzoylamino-4-oxo-1,3-dioxane system is determined by flattening of the ring lactone fragment (resulting in O(1)-sofa conformation) and characteristic twist (20 to 30°) of the planar amide group in relation to the adjacent benzene ring.
- Glowka, Marek L.,Kaminski, Zbigniew J.
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