Lewis Acid Catalyzed Reductive Cyclization of 2‐Aryloxybenzaldehydes and 2‐(Arylthio)benzaldehydes to Unsubstituted 9H‐Xanthenes and Thioxanthenes in Diisopropyl Ether

Abstract

Readily accessible 2‐aryloxybenzaldehydes and 2‐(arylthio)benzaldehydes undergo a sequence of reactions leading to a wide variety of unsubstituted 9H‐xanthenes and thioxanthenes in high yields when heated with a Lewis acid in diisopropyl ether. This reductive cyclization method is compatible with several important functional groups. The method is also applicable for the selective reductive cyclization of the more electron‐rich aryl ring of a 2,6‐bis(aryloxy)benzaldehyde. The key feature of this transformation is the chemoselective reduction of a transient xanthylium ion in the presence of aldehydic group via intermolecular hydride transfer from diisopropyl ether (solvent).

Electrochemical Regioselective Cross-Dehydrogenative Coupling of Indoles with Xanthenes

“…The compound 1- benzyl-1 H -indole 1m was synthesized by a reported method . 9 H -Xanthene reagents (except for 2j ) are known compounds, which can be prepared according to the reported methods. , The compound 2j was newly synthesized by a reported method . All the solvents were dried and freshly distilled prior to use.…”

Formation and Disproportionation of Xanthenols to Xanthenes and Xanthones and Their Use in Synthesis

“…The residue was purified by silica gel flash column chromatography (PE/EA = 10:1) to afford the desired product a . Except 14a , 17a , 19a , and 22a , other substrates are known compounds. − …”

“…Subsequently, Li and co-workers reported a metal-free oxidative coupling of a formyl C–H bond with an aromatic C–H group using tetrabutylammonium bromide (TBAB) as a promoter in aqueous medium to form xanthones . In 2020, Verma reported a Lewis acid-catalyzed reaction-formed 9 H -xanthenes and thioxanthenes . These methods generally suffer from the use of strong acids, toxic CO gas, precious metal catalysts, or harsh reaction conditions.…”

“…7 In 2020, Verma reported a Lewis acid-catalyzed reaction-formed 9H-xanthenes and thioxanthenes. 8 These methods generally suffer from the use of strong acids, toxic CO gas, precious metal catalysts, or harsh reaction conditions. Meanwhile, they represent the limit in terms of general methods to afford xanthenes directly.…”

Esters as Both Alkylating and Acylating Reagents: PCl3‐Promoted Friedel‐Crafts Reaction in One‐Pot

“…As shown in Scheme 4, initially, PCl 3 reacts with water present in air to generate PRCl(OH), which undergoes a D/H exchange reaction to provide A. A further reacts with I 2 in situ to afford DI/HI and iodophosphate B, which is attacked by 4 to yield intermediate C. [13] The subsequent dissociation of C with DI/HI forms intermediate D. Intermediate D reacts with A to generate E. A Friedel-Crafts alkylation reaction between E and arene takes place furnish the intermediate F. Next, intermediate F is converted to the corresponding acid chlorides G under this system. Finally, the Friedel-Crafts acylation reaction between G and arene affords the desired product 5.…”