Lewis Acid Catalyzed Dual Bond Formation: One-Pot Synthesis of Indenes

Indenes comprise an important class of carbocyclic compounds. Many indenes constitute a ubiquitous core structure present in several natural products of biological importance. Also, synthetically designed indenes exhibit significant pharmacological activities. Owing to their interesting features, development of synthetic strategies towards their preparation is highly desirable. Herein, we describe a simple and an effective one-pot method for the synthesis of indenes using Lewis acid catalysis. This method enables formation of two C−C bonds in a one-pot protocol from readily accessible tert-benzyl alcohols and diaryl acetylenes. The scope of the reaction has been well studied on varied tertiary alcohols from simple to electronically rich systems. The designed methodology has been effective on symmetrical and unsymmetrical alkynes. The present method involves Lewis acid in catalytic amounts, thus prevents the formation of competitive homo cyclodimerization. Significantly, a variety of indenes constituting a quaternary carbon atom were synthesized.