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

Abstract

Palladium-catalysed sequential one-pot synthesis of fluorenones is described. The reaction comprises intermolecular Suzuki coupling and intramolecular acid-mediated cyclisation in a one-pot procedure. The protocol is also applied to the synthesis of fluorenes using a single column purification.

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

“…Among these are radical cyclizations [22], Pschorr reactions [23], and diverse cycloaddition protocols [24,25]. Especially transitionmetal-catalyzed cross-coupling reactions starting from benzophenones, benzoic acids, dihalogenated benzene building blocks and others have emerged as new approaches in recent years [26][27][28]. Various approaches starting from functionalized biaryls have hereby attracted considerable interest, since the precursors are readily available by established cross-coupling reactions.…”

Palladium‐Catalyzed Suzuki Coupling and NIS‐Mediated Dehydrogenative Cylcoetherification: A Concise Approach to 6,6‐Disubstituted 6H‐benzo[c]chromenes and Total Synthesis of Didehydroconicol

“…With the synthetic plan in our hand, we initially, synthesized a variety of ortho-bromo tertiary benzylic alcohols 6 using the established literature procedures. [20,22] Next, the alcohols 6 were subjected to the little modified Suzuki coupling conditions [23] with various arylboronic acids 7 to accomplish ortho-aryl tertiary alcohols 8 (Table 1). Hence, initially, the simple ortho-bromo benzylic alcohol 6 a was tested with different arylboronic acids with varying electronic effects such as mild to strong electronreleasing groups (i. e.: Me, Et & OMe), and also to electronwithdrawing functional groups (e. g.; F, Cl, CN & NO 2 ) at various positions on the arene ring of arylboronic acid were coupled successfully and furnished the corresponding ortho-aryl-tertbenzylic alcohols 8 aa-8 ak with the yields ranging from 68 % to 90 %.…”

Sequential One‐Pot Process to Construct a Dual C−C Bond: Synthesis of Fluorenes and Total Synthesis of 4‐O‐Demethyl‐nobilone

“…Also, it was envisioned that the acidmediated intramolecular cyclization step could be facilitated by using simple, mild and inexpensive Lewis acid. Thus, unlike earlier step-wise reports, [20,22] including our report, [23] which was limited to the synthesis of fluorenones and fluorenes with a tertiary carbon atom, [23] herein, we present a sequential one-pot process for synthesizing a quaternary carbon-bearing 9,9disubstituted-9H-fluorenes via a palladium-catalyzed intermolecular Suzuki coupling of ortho-bromotertiarybenzylic alcohols and arylboronic acids, [23,24] and a mild Lewis acid promoted intramolecular Friedel-Crafts alkylation reaction. The strategy presented a broad substrate scope and furnished 9,9-disubstituted-9H-fluorenes up to excellent yields.…”

“…Thus, there is still enough room to explore and develop efficient methods for the synthesis of fluorenes. In this context, our research group in 2018, [23] presented a sequential one‐pot tactic for synthesizing fluorenones via Suzuki coupling and a strong acid (TfOH) induced intramolecular acylation pathway; also, the same report was extended to fluorenes with a tertiary carbon were achieved using a single column chromatography process through Suzuki coupling, sodium borohydride mediated reduction in one‐pot and the intramolecular alkylation of the crude secondary alcohol with BF 3 ⋅OEt 2 .…”