Chiral NMR

It has been reported that the chiral NMR shift reagent Eu(DPPM), represented by structure 19, catalyzes the Mukaiyama-type aldol condensation of a ketene silyl acetal with enantiose-lectivity of up to 48% ee (Scheme 8B1.13) [29-32]. The chiral alkoxyaluminum complex 20 [33] and the rhodium-phosphine complex 21 [34] under hydrogen atmosphere are also used in the asymmetric aldol reaction of ketene silyl acetals (Scheme 8BI. 14), although the catalyst TON is quite low for the former complex. 

In the 9-coordinate TTHA complexes of the heavier Ln + ions, the situation is more complex, since there also the terminal N-atom bearing the uncoordinated acetate moiety is chiral. NMR [49, 50], luminescence [47, 51] and NMRD measurements [46] have shown that, for both 9- and 10-coordinate Ln(TTHA) complexes, the inner coordination sphere of the metal ion is fully occupied by donating groups of the figand, leaving no space for the coordination of water. Consequently, the water proton relaxation enhancement has no inner sphere contribution and the [Gd(TTHA)] complex is not very suitable for application... 

Strains of Pseudomonas putida are very versatile in metabolizing aromatic compounds, particularly to the corresponding 1,2-dihydro-l,2-diols. The hydroxylating enzyme of the P. putida mutant is not strongly substrate specific and alkyl, aryl and halogen functionalities are usually readily tolerated380. Thus, 4-bromobenzoic acid (1, R = Br) is converted to a. v-4-bro-mo-5,6-dihydroxy-l, 3-cyclohexadiene-l-carboxylic acid (2, R = Br) in 80% yield with 98% cc (determined by chiral NMR shift experiments on the 4-nitrobenzyl ester) 375. The absolute stereochemistry, (5R,6R), was determined by a single crystal X-ray analysis. 

Achiral lanthanide chelates have been used in conjunction with other chiral NMR deriva-tizing or solvating agents. The addition of the lanthanide enhances enantiomeric discrimination and/or causes shifts in the spectrum that show a characteristic trend with absolute configuration. 

Analysis of Reagent Purity chemical purities are accessed by mp and NMR optical purities are deduced by forming diastereo-meric derivatives, or by derivatization and analysis in the presence of chiral NMR shift reagents. 

Throughout the text most, but not all, of the 60 and 90 MHz nmr spectra have been replaced with 250 MHz proton spectra. A section on 2D nmr is included in the chapter on nmr spectroscopy, and procedures are given for the use of chiral nmr shift reagents to determine the optical purity of the product from the chiral enzymatic reduction of a ketone. 

Progress has been made in the search for new lanthanide /3-diketonates as sources of luminescence, with application in the fabrication of polymer light-emitting diodes for low-cost, full-color, flat-panel displays.16,17 Moreover, some complexes seem promising as chiral NMR reagents for the determination of enantiomeric purity18,19 and prospective catalysts in many organic syntheses.20... 

This diamine has had many uses. The bis m-trilluoromethyl compound 270 made in the same way from m-trifluoromethylbenzaldehyde, is a chiral NMR shift reagent that gives better spectra than the more traditional Eu-based shift reagents and allows the reliable determination of ee. Terpenes are notorious for low ees and the ee of myrtenal 271 was determined as 96% by formation of the aminal 272 and the measurement of its 19F NMR spectrum.48 The signals for the two diastereoisomers were easily distinguished and integrated even though the compounds were difficult to separate by chiral HPLC. 

In NMR spectroscopic analysis, CDs are mainly used as chiral NMR shift reagents. The complexation with CDs can affect the character of the NMR spectra of... 

Resolved Troger s base (1) interacts with chiral alcohols as a chiral NMR shift reagent.It is also possible to use enantiopure Troger s bases for chiral resolution and chiral induction. When 1 X=H) was imprinted... 

O Farrell CM, Hagan KA, Wenzel TJ. Water-soluble calix[4]resorcinarenes as chiral NMR solvating agents forbicyclic aromatic compounds. Chirality 2009 21(10) 911-21. 

Once prepared [14], the two enantiomeric MPA polymers, poly-(f )-2 and poly-(5)-2, showed null CD spectra in a number of solvents, suggesting the presence of analogous populations of both helical senses. Thus, despite the presence of stereogenic centres at the pendants, the resulting polymer was racemic in its axial chirality. NMR, Raman and differential scaiming calorimetry (DSC) [15-18] studies pointed to cis-cisoid configurations at their polyene backbones. 

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