Nuclear magnetic resonance with electrophiles

The direct attack of proton from the solvent on the intermediate dihydropyridine as well as the over-all mechanism of the reduction received support from the extent and position of deuterium labeling in the product from the reduction of l-methyl-4-phenyl-pyridinium iodide (7) with sodium borohydride in dimethylformamide and deuterium oxide. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (9) formed was shown by nuclear magnetic resonance (NMR) and mass spectral analysis to contain approximately one deuterium atom located at the 3-position.13,14 This is the result to be expected from the pathway shown in Eq. (3) if the electrophile were a deuteron. 

A silver-silyl intermediate was detected by Si nuclear magnetic resonance (NMR) at 5 = 97 ppm and inverse saturation behavior was detected with mono-substituted alkenes. Based on their studies, a silver-mediated reversible releasing of silylene followed by an irreversible electrophilic addition of the silver-silyl intermediate to the alkene was suggested (Fig. 32). 

Infrared evidence of bond strengths and charge distributions have been compared with similar data for 1-thiocoumarin, 1-selenocoumarin, 2-thiocoumarin, and 2-selenocoumarin. ° Ultraviolet data have been correlated with extensive molecular orbital calculations. " Such calculations indicate that electrophilic substitution should occur at C-3 and nucleophilic or radical substitution at C-2. Nuclear magnetic resonance - and mass spectral data are available. As... 

The numerous reactions and physical properties that can be correlated with electronic substituent constants suggest that they reflect a basic mechanism for the effect of the substituent on the reaction or the property. Many reactions were correlated by the Hammett equation, such as electrophilic (4, 31, 32, 33), nucleophilic (4, 34) and radical (35, 36, 37). Spectroscopic properties, such as infrared and ultraviolet absorption frequencies and intensities (38). nuclear magnetic resonance shifts of various nuclei, e.g., -H, F, (39), and mass spectroscopic ionization... 

Among the most important reactions of ammonia and of amines are ammonolyses and condensations. Both start with an attack of the p electrons on an electrophilic centre, followed by the loss of one or two protons, and other transformations depending on the electrophile. These reactions are the basis of many analytical methods for amines. Other methods are based on the instability of the bond, on its abihty to form hydrogen bonds, and on its distinctive vibrational and nuclear magnetic resonance spectra. 

Alternatively, chlorotrimethylsilane can be used to react with the enolate mixture to give the corresponding enol trimethylsilyl ethers. The enol acetate or enol trimethylsilyl ether mixture can be analyzed by gas chromatography or by nuclear magnetic resonance (nmr). Table 1.2 shows the data obtained for several ketones. Some of the data were measured by the techniques just mentioned. In a number of cases the data are more qualitative and indicate the enolate which gave rise to isolated products on subsequent reaction with electrophiles. 

Ketimines and aldimines proved to be good substrates [73]. Based on the structure modification, nuclear magnetic resonance (NMR) study, kinetic study, and computational study, they proposed a double hydrogen bond structure between the acidic N-H protons and the imine lone pair to activate the electrophile toward the attack by the cyanide ion (Figure 2.15) [74]. The catalyst system is applicable to the Mannich-type reaction of N-Boc-aldimine with ketene silyl acetals to give corresponding P-amino esters in 86-98% ee (Scheme 2.25) [75]. Hydrophospho-nylation of aldimines with bis(2-nitrobenzyl)phosphite by means of (4d) furnished a-amino phosphonates in good enantioselectivity (Scheme 2.26) [76]. 

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