Nitrone Cycloadditions to 2,3-Dihydro-1-phenyl-1H-phosphole 1-Oxide. Double Asymmetric Induction and Kinetic Resolution by a Chiral Nitrone

Article abstract of DOI:10.1016/S0957-4166(00)80033-6

The cycloadditions of nitrones with 2,3-dihydro-1-phenyl-1H-phosphole 1-oxide give a single cycloadduct deriving from a highly diastereoselective approach of the nitrone anti to the phenyl ring of phospholene oxide.When the chiral gliceraldehyde derived nitrone is used, only two diastereoisomers are produced in 1.7:1 ratio.The structural assignment based on NMR data and X-ray analysis of the major isomer established a trans C3-C4 stereochemistry (derived from endo TS with respect to nitrone) and a C3-C4' relative stereochemistry of threo type in the major isomer and erythro in the minor one.Therefore, each enantiomer of phospholene oxide 6 gives exclusively one cycloadduct with five contiguous stereogenic centres in an established and predictable absolute configuration.The difference of reactivity of the two enantiomers allowed a partial kinetic resolution of the racemic phospholene oxide, affording (+)-(S) enantiomer with 90percent enantiomeric excess.