Gold(II) Chloride Catalyzed Domino Processes with Isobenzopyrylium Cation Intermediates

摘要

As a result of its synthetic potential the electrophilic cyclization of phenylacetylenes that have a carbonyl group or an imino group in the ortho position is currently a popular research topic. These reactions evidently profit energetically from the formation of heteroaromatic isoben-zopyrylium salts or isoquinolines, respectively. According to Tovar and Swager, strongly acidic conditions are crucial for the stoichiometric formation of isobenzopyrylium salts. Recently we found that in a special case weakly acidic conditions were sufficient to catalyze a domino process in which isobenzopyrylium formation was followed by an intra-molecular Diels-Alder reaction with an alkyne functionality. With gold(III) chloride as a catalyst, Yamamoto and co-workers carried out an analogous process, in which an intermolecular Diels-Alder reaction resulted in the efficient synthesis of highly substituted naphthalenes (Scheme 1).