Variable Strategy towards Carbasugars and Relatives. 6. Diastereoselective Synthesis of 2-Deoxy-2-amino-5a-carba-beta-L-mannopyranuronic Acid and 2-Deoxy-2-amino-5a-carba-beta-L-mannopyranose

Efficient, total syntheses of novel 2-deoxy-2-amino-5a-carba-β-L-mannopyranuronic acid (1) and 2-deoxy-2-amino-5a-carba-β-L-mannopyranose (2), a positional stereoisomer of validamine, have been achieved in 28% and 24% overall yields and in 12 steps and 13 steps, respectively, from 2-[(tert-butyldimethylsilyl)oxy]furan (3) and (2S)-2,3-O-isopropylideneglyceraldehyde N-benzyl imine (4) via two highly diastereoselective Mukaiyama aldol-related chemical maneuvers. The strategy, which furnishes the targeted carbasugars in enantiopure forms, allows for complete control of the configuration at all five contiguous stereocenters of the targets by utilizing the sole element of chirality present in the aldimine progenitor 4.