Lewis Acid/Brönsted Acid Mediated Benz-Annulation of Thiophenes and Electron-Rich Arenes

Abstract

A facile preparation of benz-annulated heterocycles were achieved at rt involving a Lewis acid/Brönsted acid mediated annulation of heterocycles using 2,5-dimethoxytetrahydrofuran as a four-carbon synthon. The benz-/naphth-annulation was found to be successful with electron-rich arenes as well.

Palladium(ii)-catalyzed synthesis of dibenzothiophene derivatives via the cleavage of carbon–sulfur and carbon–hydrogen bonds

“…This method can also be used for the synthesis of the benzo[ b ]thieno[3,2- d ]thiophene ring systems 22 , albeit in a lower yield than the corresponding dibenzothiophene derivatives likely because of the large angle strain associated with this target. Furthermore, this method provided facile access to dibenzoselenophene ( 23 ),14 thereby demonstrating that these palladium-catalyzed conditions can be used to activate a C–Se bond 15…”

Synthesis of Annulated Anthracenes, Carb­azoles, and Thiophenes Involving Bradsher‐Type Cyclodehydration or Cycli­zation–Reductive‐Dehydration Reactions

“…2,3‐Dimethoxyanthracene (7e): Cyclodehydration of 2‐(3,4‐dimethoxylbenzyl)benzaldehyde ( 6e ; 0.35 g, 1.36 mmol) using BF 3 · OEt 2 (0.04 g, 0.27 mmol) following a procedure similar to that described for 7a gave 2,3‐dimethoxyanthracene ( 7e ; 0.28 g, 87 %) as a colourless solid, m.p. 200–202 °C (ref 16a. 200–202 °C).…”

Annulative π‐Extension (APEX): Rapid Access to Fused Arenes, Heteroarenes, and Nanographenes

“…However, additional heteroarenes are contained in the skeletons of fused heteroarenes 103 . For simple benzannulative APEX reactions of electron‐rich heteroarenes, 2,5‐dimethoxytetrahydrofuran 104 is used as the π‐extending reagent in the presence of TfOH or ZnBr 2 to afford dibenzoheteroles 105 in high yields (Scheme ) . Furthermore, dihydrodimethoxyisobenzofuran 106 shows a good performance in the benzene‐to‐anthracene APEX reaction of electron‐rich 1,2‐dimethoxybenzene.…”