Reaction of acetyliron anion with terminal halogeno-deoxysugars

Reaction of the anion(2) generated from acetyliron complex (1) with methyl 5-bromo-5-deoxy-2,3-O-isopropylidene-beta-D-ribofuranoside (3) led to a Grob-type fragmentation of the furanoside to open-chain aldehyde (7) which, in situ, reated with 2 to form a mixture of stereoisomeric complexes 4. Decomplexation furnished methyl esters of 2,6,7-trideoxy-4,5-O-isopropylidene-heptonic acid of D-ribo and D-arabino configuration. Analogously, from methyl 2,3,4-tri-O-benzyl-6-bromo-6-deoxy-alpha-D- galactopyranoside (8) methyl 4,5,6-tri-O-benzyl-2,7,8-trideoxy-L-manno-oct-7-enoate (10) was obtained. Methyl 6-bromo (iodo)-6-deoxy-hexopyranoides 12-15 did not undergo Grob fragmentation in the presence of 2.