'High Noon'in Gold Catalysis:Carbene versus Carbocation Intermediates

摘要

In the past eight years,homogeneous catalysis of organic reactions by gold complexes has developed into a unique and highly useful tool for organic synthesis.The preparative advantages of these reactions are quite clear,but the mechanistic aspects often are not.While labeling studies,'31 the identification of side products,spectroscopy/spectrometry in situ,trapping of intermediates,and quantum chemical investigation have led to a good understanding of several reaction pathways,the electronic structure of a crucial intermediate of many reactions is still a matter of debate.Many gold-catalyzed reactions,in particular the cycloisomerizations of enynes,proceed by the initial elec-trophilic attack of a gold-alkyne complex 1 on an alkene 2,leading to the intermediate 3(Scheme 1).