Lewis Acid Mediated One‐Pot Synthesis of Aryl/Heteroaryl‐Fused Carbazoles Involving a Cascade Friedel–Crafts Alkylation/Electrocyclization/Aromatization Reaction Sequence

Abstract

A Lewis‐acid‐mediated domino reaction of 2/3‐(bromomethyl)indoles with arenes/heteroarenes led to the formation of the corresponding annulated carbazoles. This three‐step one‐pot transformation proceeds by sequential Lewis acid catalysed Friedel–Crafts alkylation, electrocyclization and aromatization reactions. The strategy is highly efficient for the assembly of complex aryl/heteroaryl‐fused carbazoles.

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

“…Aldehyde 6a also underwent a facile cyclodehydration upon treatment with BF 3 · OEt 2 (20 mol‐%) in dry CH 2 Cl 2 at room temperature to give naphtho[2,3‐ c ]carbazole 7a in a slightly better yield. The formation of naphtho[2,3‐ c ]carbazole 7a as the sole product from the cyclodehydration of aldehyde 6a is consistent with our earlier observations 16c…”

“…2‐(Thiophen‐2‐yl)naphtho[2,3‐ b ]thiophene (7j): Cyclodehydration of 2‐(2,2′‐bithiophen‐5‐ylmethyl)benzaldehyde ( 6j ; 0.2 g, 0.7 mmol) using BF 3 · OEt 2 (0.02 g, 0.14 mmol) following a procedure similar to that described for 7a gave 7j (0.17 g, 91 %) as a colourless solid, m.p. 258–260 °C (ref 16c. 258–260 °C).…”

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

“…Mohanakrishnan and co‐workers reported a series of APEX reactions of heteroarenes with diacetoxyacetal‐functionalized indolylmethyl bromide 98 , mediated by Lewis acids such as ZnBr 2 (Scheme ) ,. Not only indole but also thiophene and furan undergo this APEX process, which involves a tandem S E Ar, 1,5‐H shift, and electrocyclization sequence to afford various π‐extended heteroarenes 99 in high yields.…”

Synthesis of Linearly Fused Benzodipyrrole Based Organic Materials

“…When an N -alkyl-indole 37 was used, in combination with ZnBr 2 as a Lewis acid catalyst, indolo[3,2- b ]carbazole 38 was formed in 67%–69% yield. The bromide leaving group can also be replaced by an acetate [36]. The yield is however lower in this case (54%) (Scheme 11).…”