The advancement of NHC catalyzed C-C bond formation : application towards chromone synthesis, C-Glycosylation and total synthesis.
Date of Issue2012
School of Physical and Mathematical Sciences
Chemistry & Biological Sciences
The discovery of novel and efficient synthetic methods for carbon–carbon bond formation reactions remains the biggest challenge towards the development of sustainable chemical transformations. Organocatalysis mediated by nucleophilic molecules offer promising strategies in this aspect and have seized much attention over the last few years. Their advantages include not only atom economy and operational simplicity, but also the possibility for the development of nontraditional retro-synthetic bond disconnections. A standard example for such a strategy is the inversion of traditional reactivity of functional groups (Umpolung). Recently, this Umpolung strategy was applied enormously by using N-heterocyclic carbene (NHC). NHC is a small active molecule which pursues both novel and new type of reactivities. An immense effort has been made to develop an efficient intramolecular carbon-carbon bond formation between aldehyde and nitrile to derive 3-aminochromones in good to excellent yields using an NHC catalyst. Furthermore, this chemistry was extended to carbon-carbon bond formation between aldehyde and activated alkyne to derive 3-alkylchromones. Next, an immense effort has been made to develop a new type of C-glycosylation obtained from 2-nitroglucal based on Stetter reaction (acylanion 1,4-addition) technique using an NHC. Finally, an attempt of total synthesis of Oleuropein obtained from, NHC catalysed Claisen reaction.