Tetrahydroxylated pyrrolizidines of type 1 are of interest due to their ability to inhibit glycosidases.  A stereospecific synthesis of these pyrrolizidines is in its final stages.  Methyl-4,6-O-benzylidine-α,D-glucopyranoside is converted to compound 6 by standard procedures.  The iodine of compound 6 undergoes Zn reduction, which opens the pyranoside ring to form an aldehyde.  The aldehyde undergoes reductive amination with allylamine to produce a divinyl amine that is immediately Boc protected to yield compound 5.  Compound 5 is cyclized using Grubbs' 2^nd generation catalyst giving compound 4, and the C-5 hydroxyl of compound 4 is then converted into a benzoate using benzoyl chloride to yield compound 3.  Compound 3 is subjected to TFA, which removes the Boc protection and frees the amine.  This amine immediately attacks C-5 resulting in an intramolecular S_N2 reaction producing pyrrolizidine 2.  Pyrrolizidine 2 can then undergo stereospecific dihydroxylation followed by deprotection using H₂/Pd to yield pyrrolizidine 1.