Lewis acid stereocontrolled additions of a silyl ketene acetal to 2,3-di-O-isopropylidene-d-glyceraldehyde nitrones. Synthesis of l-isoxazolidinyl nucleosides

The reaction of O-methyl-O-tert-butyldimethylsilyl ketene acetal with N-benzyl and N-methyl-2,3-O-isopropylidene-d-glyceraldehyde nitrones in the presence of boron trifluoride etherate afforded the corresponding isoxazolidin-5-ones in excellent yields and anti-selectivities. The obtained compounds were used as key intermediates for the synthesis of isoxazolidinyl nucleosides of the l-series.