Monosaccharide modifications provide a rich avenue to implement organic transformations relevant to sugar chemistry.  Activation of a monosaccharide monomer through unsaturations and other activation-specific moieties is an optimal approach in the course to implement chosen organic transformations.  Further, the reactivities of each carbon differ subtle, and such differences become pertinent to understand how reactions on a sugar scaffold can vary greatly.  An example par excellence is the glycosidic bond stabilities on, for example, gluco- and galacto-sugars, where the later series exhibit higher reactivities to hydrolyze the glycosidic bond.  On the other hand, hard-soft acid base gradations are immensely applicable to understand the reactivity of each carbon of a sugar, as for example, the hard acidic anomeric center vs the soft acidic C-3 carbon in a sugar and respective reactivities towards a hard or soft nucleophile.  Yet another immense area of monosaccharide modifications is the endo--cyclic ring expansion, such that cyclic six-membered sugar is transformed to a cyclic seven-membered sugar.  Such transformations typically involve multiple synthetic sequence, with the facility that the intermediates allow a diversity orientation to the synthesis.  Thus, in addition to an often focused synthesis of seven-membered sugars, the intermediates of the synthesis lead to secure other modified sugars, for example, modifications at C-2, C-3 etc...  Thermal rearrangements are elegantly suitable to a monosaccharide, by which C-C bond formations could be implemented in a rather facile manner.  Such rearrangements and ring expansions can be extended to higher oligosaccharides too, that in the class of cyclic oligosaccharides.  Thus, synthesis of ring-expanded cyclic oligosaccharides is a case study, where a naturally-occurring cyclic oligosaccharide would have a congener, an un-natural, ring-expanded cyclic oligosaccharide.  Many examples that constitute several years of effort in monosaccharide modifications through expansions, shifts and rearrangements will be discussed in the presentation.References (i) Ganesh, N.V.; Jayaraman, N. J. Org. Chem. 2007 , 72, 5500-5504.  (ii) Paul, S.; Jayaraman, N. Carbohydr. Res. 2007 , 342, 1305-1314. (iii) Mukherjee, A.; Jayaraman, N. Tetrahedron 2012 , 68, 8746-8752.  (iv) Daskhan, G.C.; Jayaraman, N. J. Org. Chem. 2012 , 77, 2185-2591.  (v) Dey, S.; Jayaraman, N.  Beilstein J. Org. Chem. 2012 , 8, 522-527.  (vi) Dey, S.; Jayaraman, N. Carbohydr. Res. 2014 , In print.

Endo- and exo-cyclic modifications of monosaccharides through expansions and rearrangements

248th National Meeting (2014)

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