Nucleophile-nucleophile coupling is ac hallenging transformation in organic chemistry.Herein we present anovel umpolung strategy for a-functionalization of aldehydes with nucleophiles.T he strategy uses organocatalytic enamine activation and quinone-promoted oxidation to access O-bound quinol-intermediates that undergo nucleophilic substitution reactions.T hese quinol-intermediates react with different classes of nucleophiles.T he focus is on an unprecedented organocatalytic oxidative a-thiolation of aldehydes.T he reaction scope is demonstrated for ab road range of thiols and extended to chemoselective bioconjugation, and applicable to alarge variety of aldehydes.This strategy can also encompass organocatalytic enantioselective coupling of a-branched aldehydes with thiols forming quaternary thioethers.S tudies indicate as tereoselective formation of the intermediate followed by as tereospecific nucleophilic substitution reaction at aquaternary stereocenter,w ith inversion of configuration.

The first stereoselective organocatalyzed [3+2] cycloaddition reaction of donor-acceptor cyclopropanes is presented. It is demonstrated that by applying an optically active bifunctional Brønsted base catalyst, racemic di-cyano cyclopropylketones can be activated to undergo a stereoselective 1,3-dipolar reaction with mono- and polysubstituted nitroolefins. The reaction affords functionalized cyclopentanes with three consecutive stereocenters in high yield and stereoselectivity. Based on the stereochemical outcome, a mechanism in which the organocatalyst activates both the donor-acceptor cyclopropane and nitroolefin is proposed. Finally, chemoselective transformations of the cycloaddition products are demonstrated.

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The first asymmetric [3+2] cycloaddition of vinyl aziridines with α,β-unsaturated aldehydes, based on synergistic catalysis, is disclosed. This methodology allows the formation of attractive pyrrolidine structures in good yields (up to 84 %), moderate diastereoselectivity, and high enantioselectivity values (up to >99 % ee). Additionally, a tricyclic pyrrolidine core structure found in biologically active molecules was synthesized in a one-pot fashion by using the presented reaction concept. Finally, a mechanistic proposal is outlined.

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