Cyclization of 1-phenyl-2-propen-1-ones into 1-indanones using H-zeolite and other solid acids. The role of mono- and dicationic intermediates

Cyclization of aryl vinyl ketones into 1-indanones was previously known to proceed only in drastic acidic or superacidic conditions due to the necessity of dicationic, superelectrophilic activation of starting compounds. In this paper, we disclose that available solid acids such as HUSY–zeolite, sulfated zirconia or heteropolyacid, H3PW12O40 can be successfully applied instead of superacids to perform these and related reactions. The cases, when the effective excess of acidic sites of the solid is required to carry out the reaction, are interpreted in terms of key dicationic (superelectrophilic) intermediates on the solid.