TiCl₄-Promoted Intramolecular Friedel–Crafts Cyclization of α-Keto-phenylbutanoates: Synthesis of Substituted Indane and Indene Derivatives

Dedication

Dedicated to Professor S. Chandrasekaran, our beloved colleague, an inspirational teacher-scholar, and a pioneer, on the occasion of his 80th birthday.

Abstract

We report a TiCl₄-mediated intramolecular Friedel–Crafts type cyclization that provides convenient access to functionalized indane and indene derivatives. Reaction of α-ketoester derivatives bearing a phenylethyl side chain with 1.2 equiv of TiCl₄ in CH₂Cl₂ at −78 °C provided indanyl α-hydroxy ester in good yield. However, the reaction at −78 to 23 °C furnished the corresponding elimination product, indene derivatives as a major product. Furthermore, the reaction of the keto ester with 1.2 equiv of TiCl₄ at −78 to 23 °C afforded an interesting dimeric indanyl-indane derivative in good yield. Presumably, the dimerization reaction proceeds via TiCl₄-mediated cationic intermediate.

Keywords

TiCl₄ - Friedel–Crafts - Cyclization - Indene derivatives - α-Keto esters - Cationic reaction

Publication History

Received: 18 July 2025

Accepted after revision: 01 September 2025

Article published online:
02 October 2025

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