42937-74-6Relevant articles and documents
Stability of electron deficient activated nitronates under neutral and Lewis acid catalyzed conditions. Facile nitronate cycloaddition reactions to the magnesium alkoxides of allylic alcohols leading to isoxazolidines and isoxazolines
Kanemasa, Shuji,Kaga, Shinsuke,Wada, Eiji
, p. 8865 - 8868 (1998)
N-Methoxy-N-[bis(methoxycarbonyl)methylene]amine N-oxide and N-methoxy- N-(methoxycarbonylmethylene)amine N-oxide as electron-deficient activated nitronates, show an exceptionally high reactivity to the magnesium alkoxides of allylic alcohols. Isoxazolidines or isoxazolines are formed as cycloadducts, depending upon the substitution pattern of the allylic alcohols. When the latter C-monosubstituted nitronate is treated with a catalytic amount of boron trifluoride etherate, the corresponding nitrile oxide is smoothly generated through β-elimination of methanol.
Atropisomerism in monopyrroles
Boiadjiev, Stefan E.,Lightner, David A.
, p. 1721 - 1732 (2002)
As observed by NMR, iodopyrroles 1a and 1b (ethyl and methyl 3,5-dimethyl-4-[(1′-iodo-2′,2′-dimethyl)propyl]pyrrole-2- carboxylate) and a variety of related derivatives with iodine replaced by methoxy 2, thiomethyl 3, acetic acid esters 4, propionic acid ester 5 or malonic esters 6 exhibit restricted rotation about the C(4)-C(1′) bond due to the bulky tert-butyl group and an ortho effect from the sterically crowded 3,5-dimethylpyrrole. Most of the compounds, which are members of the rare class of atropisomers due to restricted rotation about an sp3-sp2 C-C bond, undergo diastereomeric enrichment by preparative TLC and crystallization. From dynamic NMR studies of the enriched diastereomers one can determine kinetic and thermodynamic parameters associated with the atropisomerism, e.g., ΔG? ～24 kcal/mol for 1 and 5 (313 K), ～22 kcal/mol for 3 (273 K), and ～25 kcal/mol for 6 (313 K) in C2D2Cl4 solvent.
An enantiomerically pure bilirubin. Absolute configuration of (αR,α′R)-dimethylmesobilirubin-XIIIα
Boiadjiev, Stefan E.,Lightner, David A.
, p. 2551 - 2564 (2001)
Enantiomerically pure (+)-(αR,α′R)-dimethylmesobilirubin-XIIIα 1 and its (αS,α′S) enantiomer ent-1 were synthesized in ten steps from simple precursors. Resolution was achieved at an early stage in the synthesis, with a racemic monopyrrole precursor rac-6 being converted to its amides 8 with (1S)-camphor-2,10-sultam. Resolution of 8 to 99% d.e. was accomplished in three crystallizations, and the absolute configuration of the acid 6 was deduced by X-ray crystallography of the more crystalline, diastereomerically pure amide 7. Circular dichroism spectroscopy of 1 showed intense bisignate Cotton effects: Δε435max = +344, Δε391max = -193 (CHCl3), as expected for a molecular exciton, and consistent with a P-helical intramolecularly hydrogen-bonded ridge-tile conformation. The Cotton effect magnitudes of 1 match almost exactly those found for (-)-(βS,β′S)-dimethylmesobilirubin-XIIIα 11 and (+)-(αR,β′R)-dimethylmesobilirubin-XIIIα. However, the Cotton effect of the pseudo-meso diastereomer (αR,β′S)-dimethylmesobilirubin-XIIIα 12 is not zero. Its large positive exciton couplet and 1H NMR NOE analysis confirm that an α-CH3 exerts a greater steric demand than a β-CH3 - by a factor of ～3.
Unified Strategy to Amphenicol Antibiotics: Asymmetric Synthesis of (-)-Chloramphenicol, (-)-Azidamphenicol, and (+)-Thiamphenicol and Its (+)-3-Floride
Liu, Jinxin,Li, Yaling,Ke, Miaolin,Liu, Minjie,Zhan, Pingping,Xiao, You-Cai,Chen, Fener
, p. 15360 - 15367 (2020/11/30)
The asymmetric synthesis of (-)-chloramphenicol, (-)-azidamphenicol, and (+)-thiamphenicol and its (+)-3-floride, (+)-florfenicol, is reported. This approach toward the amphenicol antibiotic family features two key steps: (1) a cinchona alkaloid derived urea-catalyzed aldol reaction allows highly enantioselective access to oxazolidinone gem-diesters and (2) a continuous flow diastereoselective decarboxylation of thermally stable oxazolidinone gem-diesters to form the desired trans-oxazolidinone monoesters with two adjacent stereocenters that provide the desired privileged scaffolds of syn-vicinal amino alcohols in the amphenicol family.
Copper-Catalyzed Carbonyl Group Controlled Coupling of Isatin Oximes with Arylboronic Acids To Prepare N-Aryloxindole Nitrones
Mo, Xue-Ling,Chen, Chun-Hua,Liang, Cui,Mo, Dong-Liang
, p. 150 - 159 (2017/11/28)
A variety of (E)-N-aryloxindole nitrones were prepared in good to excellent yields by using a copper-catalyzed coupling reaction of isatin oximes and arylboronic acids under mild conditions. Various arylboronic acids that contain sensitive functional groups were tolerated in the transformation, and detailed studies show that the carbonyl group of the isatin oximes serves as a ligand to control the formation of the (E)-oxindole nitrones. This method to prepare (E)-N-aryloxindole nitrones was easily performed on a gram scale and efficiently used to synthesize estrone-derived oxindole nitrone in high yield.
