A Versatile Route to L-Hexoses: Synthesis of L-Mannose and L-Altrose

An efficient route for the synthesis of orthogonally protected L-sugars has been opened up, starting from the heterocyclic homologating agent 1 and 2,3-O-isopropylidene-L-glyceraldehyde (2). Our synthetic path enables the synthesis of a 2,3-unsaturated-L-pyranoside, which can be suitably functionalized to afford the desired L-hexoses. In this paper, we report the synthesis of L-manno- and L-altro-pyranosides. Moreover, this strategy may be used to prepare all eight sugars and their derivatives in either enantiomeric form.