NI(II)-CATALYZED REACTIONS OF FREE D-FRUCTOSE DERIVATIVES MODIFIED ATPOSITIONS C-5 AND OR C-6/

The nickel(II) catalysed isomerisation reactions of D-fructose derivat ives modified at positions 5 and/or 6 were investigated. 5,6-Dimodifie d open-chain D-fructose derivatives as well as an open-chain derivativ e of D-xylulose reacted to give complex mixtures containing no major p roduct. 5-Modified ketohexoses invariantly were degraded to the corres ponding methyl pentonates upon loss of C-l. 6-Modified D-fructofuranos e furnished the desired rearrangement into a branched-chain derivative of D-ribose. In marked contrast to previous belief, from these result s it appears that 5-OH plays an important role in the productive co-or dination of the D-fructose derivatives to the nickel-ethylenediamine c omplexes under consideration.