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The mechanism of the asymmetric silylation of alcohols with isothiourea catalysts was studied by employing reaction progress kinetic analysis. These reactions were developed by the Wiskur group, and use triphenyl silyl chloride and chiral isothiourea catalysts to silylate the alcohols. While the order of most reaction components was as expected (catalyst, amine base, alcohol), the silyl chloride was determined to be a higher order. This suggested a multistep mechanism between the catalyst and silyl chloride, with the second equivalent of silyl chloride assisting in the formation of the reactive intermediate leading to the rate-determining step. Through the addition of additives and investigating changes in the silyl chloride, an understanding of the catalyst equilibrium emerged for this reaction and provided pathways for further reaction development.
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Varying the Electronics on Isothiourea Catalysts: Basicity, Rate, and Selectivity
Abstract Chiral and achiral substituted isothiourea catalysts were synthesized and employed in model silylation reactions to understand how changing the electronics on the catalyst core affected intermolecular interactions between catalyst intermediates and substrates, ultimately affecting selectivity and rate. Five different chiral catalysts were utilized in a silylation‐based kinetic resolution of 2‐(para substituted)phenylcyclohexanols and the rate of silylation of these same alcohols was investigated with three different achiral catalysts. Linear free energy relationships were examined, highlighting that rate and selectivity were highly dependent on the electronics of the catalyst and the substrate, and that both affected the intermolecular interactions that resulted.
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- PAR ID:
- 10633468
- Publisher / Repository:
- European Chemical Societies Publishing
- Date Published:
- Journal Name:
- European Journal of Organic Chemistry
- Volume:
- 27
- Issue:
- 44
- ISSN:
- 1434-193X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ejoc.202400641
