Umpolung Strategy for α-Functionalization of Aldehydes for the Addition of Thiols and other Nucleophiles.
Jakob BlomGabriel J Reyes-RodríguezHenriette N TobiesenJohannes N LamhaugeMarc V IversenCasper L BarløseNiels HammerMatilde RusbjergKarl Anker JørgensenPublished in: Angewandte Chemie (International ed. in English) (2019)
Nucleophile-nucleophile coupling is a challenging transformation in organic chemistry. Herein we present a novel umpolung strategy for α-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 α-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 α-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.