Polyhydroxylated pyrrolidines, III. Synthesis of new protected 2,5-dideoxy-2,5-iminohexitols from d-fructose

The readily available 3-O-benzoyl-4-O-benzyl-1,2-O-isopropylidene-β-d-fructopyranose () was straightforwardly transformed into 5-azido-3-O-benzoyl-4-O-benzyl-5-deoxy-1,2-O-isopropylidene-β-d-fructopyranose (), after treatment under modified Gareggʹs conditions followed by reaction of the resulting 3-O-benzoyl-4-O-benzyl-5-deoxy-5-iodo-1,2-O-isopropylidene-α-l-sorbopyranose () with lithium azide in DMF. O-debenzoylation at C(3) in , followed by oxidation and reduction caused the inversion of the configuration to afford the corresponding β-d-psicopyranose derivative that was transformed into the related 3,4-di-O-benzyl derivative . Cleavage of the acetonide of to give followed by O-tert-butyldiphenylsilylation afforded a resolvable mixture of and . Compound was transformed into (2R,3R,4S,5R)- () and (2R,3R,4S,5S)-3,4-dibenzyloxy-2′,5′-di-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine () either by a tandem Staudinger/intramolecular aza-Wittig process and reduction of the resulting intermediate Δ2-pyrroline (), or only into by a high stereoselective catalytic hydrogenation. When was subjected to the same protocol, (2S,3S,4R,5R)- () and (2R,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine () were obtained, respectively.