Investigation of cis- and trans-4-Fluoroprolines as Enantioselective Catalysts in a Variety of Organic Transformations
Daryl Q. J. Yap A , Raju Cheerlavancha A , Renecia Lowe A , Siyao Wang A and Luke Hunter A BA School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
B Corresponding author. Email: l.hunter@unsw.edu.au
Australian Journal of Chemistry 68(1) 44-49 https://doi.org/10.1071/CH14129
Submitted: 10 March 2014 Accepted: 12 April 2014 Published: 21 May 2014
Abstract
Stereoselective fluorination is known to rigidify the ring structure of l-proline, as a result of a combination of electrostatic and hyperconjugative effects associated with the C–F bond. This is a potential strategy for enhancing the enantioselectivity of proline-catalysed reactions. In this study, cis- and trans-4-fluoroprolines were investigated as catalysts in five different organic transformations, including examples of both enamine and iminium ion catalysis. Some significant differences in enantioselectivity were observed between the cis- and trans-isomers of the fluorinated catalysts, confirming that the ring pucker is important. However, no substantial improvements were observed relative to the parent catalyst, l-proline.
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