Gold-Catalyzed Ammonium Acetate-Assisted Cascade Cyclization of 2-Alkynylarylketones.

An ammonium acetate assisted gold-catalyzed cascade cyclization reaction of 2-alkynylarylketones is described. Under the reported conditions, a gold-catalyzed intramolecular cyclization of 2-alkynylarylketones takes place through two competing reaction mechanismsa 5-exo-dig or a 6-endo-dig cyclization-leading to two regioisomeric intermediates: isobenzofuranium or isobenzopyrylium. In the presence of ammonium acetate, the two intermediate compounds undergo further rearrangement to 2,3-disubstituted indenones and 1,3-disubstituted isoquinolines, respectively. While both reaction pathways proceed via a cyclization-rearrangement cascade, the gold-mediated 5-exo-dig process is especially notable, as it provides a novel cyclization protocol of 2-alkynylarylketones.