2-C-Formyl glycals: emerging chiral synthons in organic synthesis

Naturally occurring carbohydrates and their derivatives have been useful during the last few decades as "chiral pool" constituents in the enantioselective synthesis of biologically active natural and non-natural products. The ready availability of a wide range of carbohydrates in nature and their multichiral architecture, coupled with their well defined stereochemistry, make them attractive starting materials in organic synthesis. The synthesis of key intermediates by incorporation of suitable functional groups onto carbohydrates, which can then be further exploited, has always been a challenging task. In this context, 2-C-formyl glycals, a new class of carbohydrates incorporating an α,β-unsaturated carbonyl system, have recently emerged as potential synthons for numerous organic transformations. Four different syntheses of 2-C-formyl glycals have been reported so far. However, the importance of 2-C-formyl glycals has become well established after our development of a more general, one-step synthesis, employing the well known Vilsmeier-Haack reaction. Synthetic transformations of these 2-C-formyl glycals have resulted in a variety of new compounds of significant synthetic and biological interest. 2-C-Formyl glycals have been shown to be ideal substrates for chemo-, regio- and stereoselective glycosidation, nucleophilic addition/substitution and cycloaddition reactions. The reported syntheses and applications of these important "chiral intermediates" are presented