Ultrasounds mediated cyclization of aryl propionic acids: a new route towards indanones

Indanones are structural motifs frequently used as synthetic precursors of several biologically active both natural and pharmaceuticals compounds. The indanone plays a pivotal role in the donepezil (Aricept) mediated acetylcholinesterase (ACh) inhibition. The classical way to achieve an indanone moiety is to perform a Friedel- Craft cyclization of aryl propionic acyl chloride or Meldrum’s acids.[1] Some examples of cyclization starting from aryl propionic acids has been reported in the literature, but all the procedures need superacids catalysts [2] or drastic reaction conditions [3]. Molecular modelling studies have suggested indanone derivatives, reporting an EWG group on the aromatic cycle, as promising ACh inihibitors. An efficient ultrasounds-assisted Friedel-Craft cyclization of inactivated aryl propionic acids is presented. Ultrasounds allow to use a low amount of acid with respect to the procedures reported in the literature and to perform the reaction at room temperature or under slight heating. A comparison between the reaction performed with or without sonication shows that ultrasounds reduce the reaction time and improve the reaction yield giving rise to a pure product even in the case of strongly inactivated starting materials.