Chemistly of O-Silylated Ketene Acetals : Stereocontrolled Synthesis of 3-Benzoylamino-2,3-dideoxy-pentoses by a 1,3-Addition to Chiral Nitrones

The stereochemistry of 1, 3-addition of ketene acetals (1a, b) to the chiral nitrones (4a-d) derived from 2, 3-O-isopropylidene-D-glyceraldehyde was examined. The reaction of ketene methyl tert-butyldimethylsilyl acetal (1a) with the N-benzylnitrone (4a) produced a syn-1, 3-adduct (5a) predominantly, while the reaction of ketene tert-butyl tert-butyldimethylsilyl acetal (1b) with the N-diphenylmethylnitrone (4d) gave an anti-1, 3-adduct (5h) predominantly. These adducts were readily transformed into the corresponding 3-benzoylamino-2, 3-dideoxypentoses (10a, b).