Palladium-Catalyzed Oxidative Cross-Coupling of N-Tosylhydrazones or Diazoesters with Terminal Alkynes: A Route to Conjugated Enynes

摘要

Conjugated enynes have attracted considerable attention owing to their biological importance, their occurrence in various natural products, and their versatility as building blocks for the synthesis of organic conducting polymers. As a result, enormous effort has been devoted to the regio- and stereoselective synthesis of conjugated enynes. Among the various methods developed in the past decades for the synthesis of enynes, the metal-catalyzed dimerization of terminal alkynes is a straightforward and atom-efficient approach (Scheme 1a, R = R", R' = H). However, the complicated regio- and stereoselectivity of the dimerization process hampers the wide application of this method. Moreover, only in limited cases is the selective cross-coupling of two different alkynes possible. A solution to overcome this setback is the coupling of alkynes with structurally defined organometallic alkenes. However, organometallic substrates are usually difficult to handle and are toxic in general.