Synthesis of Polysubstituted Polycyclic Aromatic Hydrocarbons by Gold-Catalyzed Cyclization-Oxidation of Alkylidenecyclopropane-Containing 1,5-Enynes

A gold-catalyzed tandem cyclization oxidation of alkylidenecyclopropane-containing 1,5-enynes with 3,5-dibromo-pyridine N-oxide via a noncarbene model was developed, providing a range of synthetically valuable and useful arylacetaldehyde derivatives in moderate to good yields without oxidation of alkynes. Moreover, the corresponding aldehydes can be further transformed into polycyclic aromatic hydrocarbons in the presence of a catalytic amount of Lewis acid In(OTf)(3). The reaction represents an example of gold-catalyzed halide-free Kornblum-type oxidation through the oxidation of the cyclopropane moiety.