Study of the geometrical structures of substituted N-trimethylsilyloxyisoxazolidines

Abstract

1. Three methods have been proposed for determining the geometrical structures of the N-trimethylsilyloxy-3,5-substituted isoxazolidines, these involving study of the stereochemical variation of\(J_{15_{N,H} } \) and\(^4 J_{_{CH_3 ,H} } \) and analysis of the PMR spectra obtained in the presence of paramagnetic lanthanide complexes. 2. As a rule, it is the exo approach of the olefin to the 1,3-dipole which is realized in the cycloaddition of nitronic acid silyl esters to styrene and methylacrylate. 3. The free electron pair of the nitrogen in N-trimethylsilylisoxazolidines is pseudoequatorially oriented. 4. Isomerization of the cycloadducts of the nitronic acid silyl esters can be described as an inversion-with-buckling process. 5. The nitronic acid silyl esters with nonequivalent substituents at the carbon atom exist as equilibrium mixtures of cis and trans isomers with the latter predominant.