Stereochemical relay through oligoureas 23/06/2005 1, 21+6n Diastereoselectivity.

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Presentation transcript:

Stereochemical relay through oligoureas 23/06/2005 1, 21+6n Diastereoselectivity

Effect of the chiral sulfoxide

n = 1 : Distinguishable diastereomers n = 2 : not effect on the d 3 -isopropyl 73.5 ee% Still an equilibrium between the two helices

What is the problem ? The sulfoxide controls the first axisThe first urea doesn't control the next one

How to solve it ? Is the R group can drive the equilibrium to only one helix ??? Calculation using Spartan (density functional level) shows a minimum energy for the helicoidal structure First answer :

How to introduce the R group ?

When the urea are connected on ortho Broad signals Diastereotopic CH 3 Crystallisation in a chiral space group