The origin of enantioselectivity in photochemical reactions with diarylprolinol silyl ether catalysts

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• Ching Ching Lam, University of Cambridge
• Wednesday 26 January 2022, 14:30-15:00
• via zoom .

If you have a question about this talk, please contact Lisa Masters.

First Year PhD Report https://zoom.us/j/97542686010?pwd=OHY3Mzd6NUptaHpzTDJkOUY2QTFzZz09 Meeting ID: 975 4268 6010 Passcode: 417918

Diarylprolinol silyl ethers are important organocatalysts that enable stereoselective functionalisation at positions neighbouring the carbonyl group. However, applications of the catalysts in photochemical pathways have not yet been widely explored. Here, the stereoselective photochemical synthesis reaction of 1,4-dicarbonyls with diarylprolinol silyl ether catalysts was studied with force field and density functional theory calculations. A procedure has been developed for investigations of large and flexible chemical systems based on the conformation labelling system, ONIOM calculations and Python scripting. The procedure allows efficient and effective use of computational resources and tackles the challenges in processing outputs from conformational searching calculations.

We explain the enantioselectivity from the perspective of conformational changes and structural deformations based on the radical addition step of the reactions. The iminium in the most stable SR transition state (TS) takes up the conformation of the most stable ground state iminium (EE). The iminium diene in the SS TS adopts an EZ conformation to avoid potential structural deformations due to radical attacks from the more sterically hindered position. For systems with simpler catalysts, the iminium is EE for both, as the steric hindrance imposed by the substituent is not sufficient to cause this large structural deformation, and so the reaction shows poor enantioselectivity.

This talk is part of the Theory - Chemistry Research Interest Group series.

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