Several sugars with conjugated unsaturation (dienes or α, β‐unsaturated carbonyl compounds) have been synthesised by use of Wittig reactions. Keto‐sugars bearing a carbonyl group α to a furanose ring are prone to undergo an elimination leading to conjugated unsaturated systems. This constitutes a novel kind of side‐reaction in the application of Wittig reactions to carbonyl sugars. The synthesis of a new kind of acetylenic sugar is also described.

Some reactions of 3‐O‐alkyl‐6‐deoxy‐1,2‐O‐isopropylidene‐α‐D‐xylo‐hexofuranos‐5‐uloses (1 and 2) with Wittig reagents are described. These ketosugars react with methylenetriphenylphosphorane and benzylidenetriphenylphosphorane to give the expected unsaturated branched‐chain sugars and dienes formed by elimination of H–C(4) and the 3‐alkyloxy group. Structural studies on all these compounds have been effected using NMR. spectroscopy and particularly, when necessary, nuclear Overhauser Effect. One important by‐product of these reactions is an unsaturated ketone 3,6‐dideoxy‐1,2‐O‐isopropylidene‐α‐D‐glycero‐hex‐3‐enofuranos‐5‐ulose (6). Compounds 1 and 2 do not react with cyanomethylenetriphenylphosphorane.

Furanosen, die eine Carbonylfunktion enthalten, reagieren mit Phosphoryliden unter Bildung ungesättigter Derivate.

No abstract

No abstract