2- Oxazolin-5-ones sodium borohydride

Tetroses and Pentoses - 4-0- -Butyldimethylsilyl-2,3-0-isopropylidene-L-threose (1) has been prepared in seven efficient steps from o-xylose. 3,4-0-Isopropylidene-D-eythrulose (4) has been synthesized from the known tetritol derivative 2 by primary protection as the silyl ether 3, followed by Dess-Martin oxidation and desilylation. Compound 2 was derived from D-isoascorbic acid (see Vol. 22, p. 178, refs. 9,10). In a similar reaction sequence, the enantiomer 5 has been obtained from L-ascorbic acid. The dehomologation of several di-0-isopropylidenehexofuranoses e.g., 6- 7) has been carried out in two steps without intermediate purification, by successive treatment with periodic acid in ethyl acetate, followed by sodium borohydride in ethanol. Selective reduction of 3-deoxy-D-g/jcero-pentos-2-ulose (8) to 3-deoxy-D-g/> cero-pent-2-ose (9) has been achieved enzymically with aldose reductase and NADPH." 4-Isopropyl-2-oxazolin-5-one (10) is a masked formaldehyde equivalent that is easily converted to an anion and demasked by mild acid hydrolysis. One of the three examples of its use in the synthesis of monosaccharides is shown in Scheme 1. ... 

There are relatively many stereoselective synthetic methodologies for synthesizing these compounds. The one reported by Bundle and co-workers takes advantage of the synthetic utility of functionalized 1,2-oxazolines (Scheme 9). The synthetic sequence requires a stereoselective opening of 1,2-oxazoline with the formation of methyl 2-aminoglucoside in the pyranose form. The C-3 mesylated derivative after deprotection of 5,6-diisopropylidene functionality can be easily converted to epoxide, which can also be stereoselectively opened with an azide anion to form C-4 axial azide. C-6 mesylation of azide, followed by its reduction with sodium borohydride/nickel chloride produces methyl 2-amino-4-acetamidogulopyranoside. 

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