Sugars aziridine derivatives

The bicyclic azetidinium salts 67 were formed by intramolecular ring closure of 5-mesylates 66, even when competitive aziridinium salt formation could have occurred (Scheme 20). The pyrrolidinium salts 68 were obtained similarly. Compounds 67 and 68, with X=F or OMs, were isolable solids. Synthesis of amino-fluoro-sugar derivatives from Al-tosyl-aziridine derivatives is covered in Chapter 8 and 19. 

The conversion of azidoformates to fused-ring aziridines via the thermal generation of a nitrene has previously been reported. More recently, the photolytic conversion of a sugar-derived azidoformate has been used to prepare fused-ring aziridines <06JOC8059>. Photolysis of azidoformate 66 at 254 nm provides aziridine 67 in excellent yield. The resulting bicyclic aziridine was reduced to provide oxazolidinone 68 in 95% yield. Oxazolidinone 68 was subsequently converted to L-daunosamine. 

The endo-spiro-OZT could be prepared through a reaction sequence similar to that applied for the exo-epimer, with spiro-aziridine intermediates replacing the key spiro-epoxides (Scheme 18). Cyanohydrin formation from ketones was tried under kinetic or thermodynamic conditions, and only reaction with the d-gluco derived keto sugar offered efficient stereoselectivity, while no selectivity was observed for reaction with the keto sugar obtained from protected D-fructose. The (R) -cyanohydrin was prepared in excellent yield under kinetic conditions (KCN, NaHC03, 0 °C, 10 min) a modified thermodynamic procedure was applied to produce the (S)-epimer in 85% yield (Scheme 18). 

J.-M. Bourgeois, Synthese de sucres amines ramifies. IV. Synthbse de quelques derives nouveaux par I intermddiaire d une hexose-spiro-aziridine, Helv. Chim. Acta 59 2114 (1976). R. J. Alves, S. Castillon, A. Dessinges, P. Herczegh, J. C. Lopez, G. Lukacs, A. Olesker, and T. T. Thang, A route to functionalized branched-chain amino sugars via nitrous acid promoted spiroaziridine formation, 7. Org. Chem. 53 4616 (1988). 

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