Novel Umpolung Strategy for α‐Functionalization of Aldehydes for the Addition of Thiols and other Nucleophiles
2019
Nucleophile-nucleophile coupling is a challenging transformation in organic chemistry. Herein we present a novel umpolung strategy for alpha-functionalization of aldehydes with nucleophiles. The strategy uses organocatalytic enamine activation and quinone-promoted oxidation to access O-bound quinol-intermediates that undergo nucleophilic substitution reactions. These quinol-intermediates react with different classes of nucleophiles. The focus is on an unprecedented organocatalytic oxidative alpha-thiolation of aldehydes. The reaction scope is demonstrated for a broad range of thiols and extended to chemoselective bioconjugation, and applicable to a large variety of aldehydes. This strategy can also encompass organocatalytic enantioselective coupling of alpha-branched aldehydes with thiols forming quaternary thioethers. Studies indicate a stereoselective formation of the intermediate followed by a stereospecific nucleophilic substitution reaction at a quaternary stereocenter, with inversion of configuration.
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