Gold Vinylidene Complexes: Intermolecular C(sp~3)—H Insertions and Cyclopropanations Pathways

摘要

The most common reactivity pattern for gold-catalyzed transformations is the inter- or intramolecular attack of a nucleophile on a multiple bond which is activated by incoordination to a gold catalyst. This situation opens up an immense spectrum of useful transformations for organic chemists. Early this year, Zhang's group and our group independently reported on a new activation mode which comprises a dual role of the gold catalyst (Scheme 1). While one molecule of gold catalyst activates an alkyne by the established π-activation mode, a second gold complex [LAu~+] activates a terminal triple bond by formation of a gold(I) acetylide, which changes the whole reaction pathway. Highly reactive digold intermediates II with a gold(I) vinylidene substructure are formed and open up entirely new reaction pathways (Scheme 1). So far, fulvene derivatives l and 2 were accessible by intramolecular sp~3 and sp~2 insertion pathways. Furthermore, the conversion of bis-terminal alkynes selectively delivered the β-substituted naphthalene product 3. In this case even an intermolecular reaction of the vinylidene intermediate with the solvent benzene was possible. These results encouraged us to explore further possible transformations of intermediate II in intermolecular reactions. The results of these studies are summarized herein.