Strategies for Asymmetric Carbonyl Olefination

The first approach is based on differentiation of enantiotopic carbonyl groups in symmetrical molecules such as meso compounds, and is therefore referred to as the desymmetrization of symmetric organic molecules. Discrimination of the n-faces of symmetrically substituted carbonyl groups constitutes the second type of approach leading to dissymmetric compounds having axial chirality, and is referred to as dissymmetrization. The third type of asymmetric carbonyl oiefination 

Optically Active Phosphorus or Arsenic Reagents Used in Asymmetric Carbonyl Olefination 

It was observed that a small structural change in the phosphorus reagent can lead to the opposite sense of preferential absolute stereochemistry in the products, 

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