Presentation on theme: "Stereochemical relay through oligoureas 23/06/2005 1, 21+6n Diastereoselectivity."— 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