Nitronates spectroscopic data

For acyclic nitronates, the reaction rate can depend on the configuration of the dipole. On the basis of 15N NMR spectroscopic data, it was demonstrated (338a) that thermodynamically more favorable lruns isomers of nitronates (1) are much less reactive in [3+ 2]-addition to methyl acrylate (Scheme 3.128). 

Interestingly, the reaction of nitronate MeCBr = N(0)0SiMe2Bu with DMAD also produces substituted dihydroisoxazole (175) in good yield rather than the corresponding isomeric aziridine (176) (Scheme 3.136), which was confirmed by IR spectroscopic data (87). 

The spectroscopic data for alkyl nitronates follows very closely to those of silyl nitronates. The C=N stretching frequencies for five- and six-membered, cyclic... 

The spectroscopic data for alkyl nitronates correlate well to that of silyl nitronates, indicating that the nature of the nitronate substituent has a negligible... 

It was not possible from the spectroscopic data available to decide if the anti isoxazolidines 8 obtained from the 3 -acetoxy-iV-methyl- (or phenyl) nitrone and AT-arylmaleimide corresponded to anti-syn isomer 8 or to anti-anti isomer 8 and if the syn isoxazolidines 6, which have been isolated from the cycloaddition of the 3 -hydroxy-iV-methylnitrone to iV-arylmaleimide corresponded to syn-syn isomer 6 or syn-anti isomer 6, respectively. 

During the period of more than four decades of extensive development of chemistry of covalent nitronates, at least a thousand of these compounds have been synthesized. Their overwhelming majority has been spectroscopically characterized. Hence, a consideration of all spectral characteristics of these products within the framework of this short section is of no significance, the more so as some data have been summarized in a recent monograph 3. 

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