[Pd]‐Catalyzed Intermolecular Coupling and Acid Mediated Intramolecular Cyclodehydration: One‐Pot Synthesis of Indenes

Abstract

An efficient one‐pot synthesis of indenes from simple starting materials is presented. This process involves a dual C–C bond formation through an intermolecular Heck coupling reaction followed by acid‐mediated intramolecular cyclodehydration. The strategy is amenable to various substituted aromatics to give indenes. In addition, the regioselective synthesis of benzyl styrenes in a single column purification technique through in‐situ reduction of Heck products (ketones) followed by acid mediated dehydration of crude reaction mixture is presented.

Recent Advances in the Synthesis of Indenes

“…Another efficient one‐pot synthesis of indenes 85 through an intermolecular Heck coupling reaction followed by acid‐mediated intramolecular cyclodehydration was presented by Satyanarayana . The indene synthesis was performed from simple and readily available starting materials, allylic alcohols 83 and iodobenzenes.…”

“…Propargylic carbonates 80 were converted into allenes 81 via Pd- Another efficient one-pot synthesis of indenes 85 through an intermolecular Heck coupling reaction followed by acidmediated intramolecular cyclodehydration was presented by Satyanarayana. [43] The indene synthesis was performed from simple and readily available starting materials, allylic alcohols 83 and iodobenzenes. The reaction proceeded smoothly with highly electron-rich iodoarenes, but was unsuccessful with deactivating F and Cl groups on iodoarene.…”

Palladium-Catalysed Coupling and Acid-Mediated Cyclisation: Synthesis of Fluorenones and Fluorenes

“…Since most of such acid mediated reactions have been carried out in halogenated solvents, we decided to carry out both reactions in 1,2-dichloroethane (DCE). 19 Therefore, to the biaryl Suzuki product 3aa formed in DCE, TfOH was added and the mixture was heated at 80 °C, giving the desired product fluorenone 4aa in 58% yield (entry 9). Acylation with conc.…”

Single‐Column‐Based Heck Coupling, Condensation and Alkylation Strategy: Synthesis of 2‐Benzoyl‐2‐alkyl‐2,3‐dihydro‐1H‐inden‐1‐ones

“…The Heck reaction is known for its efficient C−C bond formation through the coupling between organic halides and olefins, using pallidum acetate as a conventional source for palladium, which presents a convenient method for carbon‐carbon bond formation at the unsubstituted vinylic position [23–26] . When allylic alcohols are used as a source of olefins with aryl halides, the Heck reaction is known to form carbonyl compounds [27] .…”

“…[22] The Heck reaction is known for its efficient CÀ C bond formation through the coupling between organic halides and olefins, using pallidum acetate as a conventional source for palladium, which presents a convenient method for carboncarbon bond formation at the unsubstituted vinylic position. [23][24][25][26] When allylic alcohols are used as a source of olefins with aryl halides, the Heck reaction is known to form carbonyl compounds. [27] Although there has been a reasonable quantum of research on the synthesis of 1,3-diketones via the aforementioned strategies, there hasn't been much development on the same through the process of palladium-catalyzed coupling reactions, especially the indanone derivative of 1,3diketone.…”