Synthesis of indenes from phenylpropanones using alumina catalyst

Abstract

1,3-Diphenylpronan-2-one undergoes dehydration over alumina at around 400° C to form 1,3-diphenylallene which cyclizes to 2-phenylindene. Since the parent ketone can be obtained under the reaction conditions from phenylacetic acid, the present reaction forms a one step syntheses of 2-phenylindene from phenylacetic acid. 3- and 4-methylphenylacetic acids also give the corresponding indenes. 1,3-Diphenylpropan-1-ones also give phenylindenes, presumably by a direct cyclodehydration reaction.