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SUMMARY:The origin of enantioselectivity in photochemical reactions with d
 iarylprolinol silyl ether catalysts - Ching Ching Lam\, University of Camb
 ridge
DTSTART:20220126T143000Z
DTEND:20220126T150000Z
UID:TALK167861@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Diarylprolinol silyl ethers are important organocatalysts that
  enable stereoselective functionalisation at positions neighbouring the ca
 rbonyl group. However\, applications of the catalysts in photochemical pat
 hways have not yet been widely explored. Here\, the stereoselective photoc
 hemical synthesis reaction of 1\,4-dicarbonyls with diarylprolinol silyl e
 ther catalysts was studied with force field and density functional theory 
 calculations. A procedure has been developed for investigations of large a
 nd flexible chemical systems based on the conformation labelling system\, 
 ONIOM calculations and Python scripting. The procedure allows efficient an
 d effective use of computational resources and tackles the challenges in p
 rocessing outputs from conformational searching calculations.\n\nWe explai
 n the enantioselectivity from the perspective of conformational changes an
 d structural deformations based on the radical addition step of the reacti
 ons. The iminium in the most stable SR transition state (TS) takes up the 
 conformation of the most stable ground state iminium (EE). The iminium die
 ne in the SS TS adopts an EZ conformation to avoid potential structural de
 formations due to radical attacks from the more sterically hindered positi
 on. For systems with simpler catalysts\, the iminium is EE for both\, as t
 he steric hindrance imposed by the substituent is not sufficient to cause 
 this large structural deformation\, and so the reaction shows poor enantio
 selectivity.\n
LOCATION:via zoom 
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