Lewis base catalyzed enantioselective oxysulfenylation of alkenes

Catalysis;Lewis Bases;Enantioselecive;Organocatalysis

Kornfilt, David Jean Pierre

关键词: Catalysis;    Lewis Bases;    Enantioselecive;    Organocatalysis;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/95493/KORNFILT-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The Lewis base activation of Lewis acids has been harnessed in the development of an enantioselective oxysulfenylation reaction for unactivated alkenes. The weak Lewis acid N-(phenylthio)-phthalimide can be activated in the presence of a moderate Brønsted acid and chiral Lewis base donors. The resulting complex is a powerful sulfenylating agent capable of sulfenium transfer to simple mono-, di- and trisubstituted alkenes with high selectivity to form enantioenriched thiiranium ions. Stereospecific and site-selective capture of the thiiranium ions furnish vicinally functionalized thioethers. The nucleophile scope of the reaction encompasses alcohols, carboxylic acids and phenols. Both inter- and intramolecular sulfenylation reactions were realized. The reaction is highly robust and individual substrates usually did not require reoptimization.Mechanistic, X-ray crystallographic and kinetic investigations enabled a complete catalytic cycle to be formulated. The proposed cycle was supported by both kinetic data and the characterization of reaction intermediates. The turnover-limiting and enantiodetermining steps were identified as thiiranium ion formation. X-ray crystallography of the active sulfenylating agent did not immediately identify a basis for the high selectivity. Instead, the origin of selectivity in the reaction of trans-alkenes was determined to be distortion-based with the aid of computational models.