Synthesis of Xanthones, Thioxanthones, and Acridones by the Coupling of Arynes and Substituted Benzoates

Abstract

The reaction of silylaryl triflates, CsF, and ortho-heteroatom-substituted benzoates affords a general and efficient way to prepare biologically interesting xanthones, thioxanthones, and acridones. This chemistry presumably proceeds by a tandem intermolecular nucleophilic coupling of the benzoate with an aryne and a subsequent intramolecular electrophilic cyclization.

Orthogonal Synthesis of Fluorinated Acridones and Acridines from Perfluorobenzophenone

“…Recently, a new approach based on an annulation reaction utilizing salicylates and silylaryl triflates plus CsF has been presented. [14] However, harsh reaction conditions and multistep procedures are generally required. [15] Within this frame, fluorinated acridines and acridones form an interesting group of compounds with applications as fluorophores for biological probes and in materials science.…”

Synthesis of toxyloxanthone B

“…In common with many other routes to xanthones, the synthesis of toxyloxanthone B trimethyl ether 3b was achieved in a classical sense by way of a suitably substituted benzophenone, 16 but we were attracted by the more contemporary aryne-based method introduced by Larock. 19,20 There has been a recent resurgence in interest in aryne chemistry, and their application in natural product synthesis is extremely topical. 21e23 The…”

“…17,18 Surprisingly, despite their relative structural simplicity, a-mangostin 1 is the only one of the three compounds to be synthesized. 8 We now report the synthesis of toxyloxanthone 3 that not only constitutes the first synthesis of the natural material, but also, as far as we are aware, illustrates the first use of the aryne-based methodology developed by Larock 19,20 in the synthesis of bioactive natural products.…”

4.09 Nucleophilic Coupling with Arynes

“…The versatility of the annulation method has been further improved by employing 2-(trimethylsilyl)aryl triflates as an aryne precursor: variously substituted xanthones 67, thioxanthones 68, and acridones 69 are facilely available from benzoates having a nucleophilic heteroatom (O, S, or N) at the ortho-position (Scheme 60), 197,198 and replacement of the electrophilic ester moiety into acyl, 199 formyl, 200 or electron-deficient alkenyl 201 group enhances the molecular diversity of the resulting six-membered heterocycles (Scheme 61).…”