A new total synthesis of D-threo-L-talo-Octose

Article abstract of DOI:10.1002/hlca.19910740307

A new approach to the total, asymmetric synthesis of D-threo-L-talo-octose ((-)-1) and its derivatives is presented. It is based on the chemoselective Wittig-Horner monoolefination of a 5-deoxy-D-ribo-hexodialdose derivative 4 obtained by selective reduction of (-)-5-deoxy-2,3-O-isopropylidene-β-D- ribo-hexofuranurono-6,1-lactone ((-)-3). Allylic bromination of the resulting methyl (E)-oct-6-enofuranuronate (+)-5 followed by intramolecular nucleophilic displacement of the so-obtained bromides gave a 13.3 :1 mixture of (-)-methyl (E)-1,4-anhydro-6,7-dideoxy-2,3-O-isopropylidene-β-L-talo-oct-6- enopyranuronate ((-)-8) and methyl (E)-1,4-anhydro-6,7-dideoxy-2,3-O- isopropylidene-α-D-allo-oct-6-enopyranuronate (9). The double hydroxylation of the enoate (-)-8 followed Kishi's rule and gave the corresponding D-threo-β-L-talo-octopyranuronate derivative (-)-11 with a good diastereoselectivity. Reduction of ester (-)-11 and deprotection led to pure (-)-1.