''Naked Sugars''as Synthetic Intermediates. Total Synthesis of L-Daunosamine

Article abstract of DOI:10.1021/jo00376a055

The ''naked sugars'' are optically pure synthetic intermediates.Their advantage compared with natural sugars is that they possess a number of unsubstituted carbon atoms that can be substituted stereospecifically through direct procedures. (1S,2R,4S)-2-<(-)-Camphanoyloxy>-7-oxabicyclo<2.2.1>hept-5-ene-2-carbonitrile ((+)-1) is an example of a ''nuked sugar''.Electrophilic reagents add to the C(5), C(6) double bond, giving the corresponding adducts where the electrophile substitutes the exo position of C(6) and the nucleophile the endo position at C(5).This principle was used to prepare (1R,4R,5R)-5-endo-chloro-7-oxa-2-bicyclo<2.2.1>heptanone (13), which was monomethylated stereoselectively in the exo position at C(3), giving (+)-(1R,3S,4R,5R)-5-endo-chloro-3-exo-methyl-7-oxa-2-bicyclo<2.2.1>heptanone (14).The latter was transformed stereospecifically indo L-daunosamine (3-amino-2,3,6-trideoxy-L-lyxo-hexose).The (-)-camphanic acid used to engender asymmetry was recovered at an early stage of the synthesis.