Unstable £>-mannose derivative

Similar protocol was applied in the first total synthesis of KDN from non-carbohydrate sources [138]. Catechol derivative 228 was transformed into protected tetraol 235, according to the literature method [139] (Scheme 51). This, in turn, underwent smooth ozonolytic cleavage to give after reductive work-up the ester alcohol, which was converted, over three steps, into the unstable D-mannose derivative 236. Reaction of compound 236 with pyruvate anion equivalent gave a syn product 237, accompanied by the another isomer (3 2). Conversion into KDN was performed in two steps involving ozonolytic cleavage of the double bond, then deprotection with concomitant cyclization using TFA-water mixture. 

Migration of the ring-oxygen atom also occurred predominantly in the deamination of the tetra-O-acetyl derivatives of 2-amino-2-deoxy-a- and -/3-D-glucopyranose to give 3,4,6-tri-0-acetyl-2,5-anhydro-D-mannose (10), which is unstable and readily eliminates acetic acid to... 

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