OPTICALLY-ACTIVE TRICARBONYL(ETA(6)-O-TRIMETHYLSILYLBENZALDEHYDE)CHROMIUM(0) COMPLEXES IN ORGANIC-SYNTHESIS - A HIGHLY DIASTEREOSELECTIVE 1,3-DIPOLAR CYCLOADDITION WITH ELECTRON-RICH OLEFINS

Heating of a racemic nitrone 2, derived from tricarbonyl(eta6-o-trimethylsilylbenzaldehyde)chromium(0) complex 1, with electron-rich olefins gave after decomplexation the cis-3,5-disubstituted isooxazolidines in a highly stereo- and regio-selective manner. Similarly, high selectivities were observed when the nitrone 9 possessing no silyl group at the ortho position on its benzene ring was employed instead of 2. The corresponding non-complexed nitrones were found to provide the cis-isoxazolidines in a moderately selective fashion or the trans-ones predominantly. Treatment of chiral 2 with electron-rich olefins afforded the corresponding chiral cis-3,5-disubstituted isoxazolidines exclusively. The enantiomeric excess for cycloadducts thus obtained was determined to be 96- > 98%. The absolute configuration of these optically active isoxazolidine derivatives was established on the basis of an X-ray crystallographic analysis.