Electrophilic activation and cycloisomerization of enynes: a new route to functional cyclopropanes

Transformations of enynes in the presence of transition-metal catalysts have played an important role in the preparation of a variety of cyclic compounds. Recent developments in the activation of triple carbon-carbon bonds by electrophilic metal centers have provided a new entry to the selective synthesis of cyclopropane derivatives from enynes. The mechanisms of these reactions involve catalytic species with both ionic and cyclopropylcarbenoid character. This type of activation will undoubtedly be further developed for application to other unsaturated hydrocarbons and inspire new catalytic cascade reaction sequences. This Minireview discusses the recent developments in electrophilic activation of enynes and shows that simple catalysts such as [Ru(3)(CO)(12)], PtCl(2), and cationic gold complexes are efficient precursors to promote the formation of functional polyclic compounds.