Reductive ring opening acetals, selective protection

Besides being useful for selective protection of monosaccharides, cyclic acetals can display a number of interesting reactions, such as reductive or oxidative ring opening, that amplify the synthetic interest of these protecting groups [125]. 

The former synthesis proceeds via epoxide 278 which was ring opened by azide, the resulting alcohol was protected and full reduction of the lactone and mesylation gave 279. Reductive cyclization and deprotection then provided 280 (Scheme 23). The 6-epi analogue 111 was prepared by converting 275 to pyrrolidine 276. Selective acetal removal and primary hydroxyl mesylation then allowed reductive cyclization followed by deprotection to give 277. Similar chemistry was also used to convert 281, closely related to 275, to (2R)-2-hydroxy-6-e/ /-castanospermine 282. ... 

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