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Absolute control of stereochemistry
09 June 2008
The one-step synthesis using an organocatalyst to control six chiral centres in a single molecule has been reported by Danish chemists.
It has always been a challenge to get the stereoisomer you want in organic chemistry - and reactions that control the stereochemistry have become valuable tools for organic chemists. Key to this is organocatalysis - the use of organic molecules as catalysts. These have all the benefits of traditional catalysts, without using expensive (and often toxic) metals.
The organocatalyst directs the synthesis to make just 1 out of 64 possible stereoisomers
Karl Anker Jørgensen and colleagues from the University of Aarhus, Denmark, have now controlled the formation of no fewer than six stereocentres in a single reaction, using the power of simple organocatalysts. This, says Jorgensen, equates to the selective synthesis of just one out of 64 possible stereoisomers, and 'takes organocatalysis to a new level'. They studied the condensation of three molecules - an unsaturated aldehyde and two tricarbonyl compounds - to give a fused ring system.
Using achiral starting materials and a chiral organocatalyst, an enantiomerically-pure silylated hydroxyamine, just one product was formed, with its absolute stereochemistry controlled at all six centres. Jørgensen says that by testing the limits of our catalysts in this way, 'we learn about catalytic systems and can use this knowledge in the design of new and improved catalysts'. He says the ultimate aim is to mimic Nature, which can often create several stereocentres simultaneously.
'This fascinating research', says Ben Feringa from the University of Groningen, The Netherlands, 'again shows the power of organocatalysis, and might well set the stage for new ways to approach total synthesis in the future'.
Link to journal article
Controlling the formation of 1 out of 64 stereoisomers using organocatalysis
Søren Bertelsen, Rasmus L. Johansen and Karl Anker Jørgensen, Chem. Commun., 2008, 3016
Also of interest
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