Tosylhydrazones: New Uses for Classic Reagents in Palladium-Catalyzed Cross-Coupling and Metal-Free Reactions

Tosylhydrazones are useful synthetic intermediates that have been used in organic chemistry for almost 60 years. The recent discovery of a palladium-catalyzed cross-coupling reaction involving a tosylhydrazone coupling partner has triggered renewed interest in these reagents. This reaction shows nearly universal generality with regard to the hydrazone and can be employed for the preparation of polysubstituted alkenes. In the course of this research, novel metal-free Ci-C and Ci-O bond-forming reactions have been discovered. Since tosylhydrazones are readily prepared from carbonyl compounds, these transformations offer new synthetic opportunities for the unconventional modification of carbonyl compounds. This Minireview discusses all of these new reactions of a classic reagent. Never too old to rock 'n' roll: The investigation of tosylhydrazonesa - widely used intermediates in organic synthesisa - as coupling partners in palladium-catalyzed and metal-free cross-coupling reactions has led to the discovery of powerful Ci-C and Ci-O bond-forming transformations. These reactions offer novel possibilities for the unconventional modification of carbonyl compounds (see examples of product types; Ts=p-toluenesulfonyl). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.