A novel one pot synthesis of calothrixin B and its analogs is achieved involving an FeCl3-mediated domino reaction of enamines in dry DMF at reflux. Alternatively, the enamines upon interaction with CuBr2 in DMF at reflux led to the formation of 1-phenylsulfony-2-(2'-nitroaryl)-4-hydroxycarbazole-3-carbaldehydes in excellent yields.

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.

The total synthesis of calothrixin B and its analogs was achieved starting from 2‐methylindole. The synthesis involved an electrocyclization of 2‐nitroarylvinyl‐3‐phenylsulfonylvinylindoles as a key step to give 2‐nitroaryl‐4‐methoxy‐3‐methylcarbazoles. Oxidation of these compounds followed by reductive cyclization led to N‐phenylsulfonylquinocarbazoles. These quinocarbazoles underwent hydrolysis and aerial oxidation in one pot to give the target compounds.

A straightforward synthesis of aryl and heteroaryl-annulated cyclo[b]carbazoles has been developed via SnCl4-mediated one-pot arylation, cyclization and aromatization reaction sequence from 3-acetyl/aroyl-2-pivaloyloxymethylindoles. The starting material is easily accessible from commercially available 2-methylindole via Friedel-Crafts acylation, bromination and pivaloylation. Remarkably, electron withdrawing/donating aroyl units including heterocyclic systems are well tolerated in the present domino reaction protocol. Furthermore, this methodology could be extended to the synthesis of dibenzofurocarbazole via bis-annulation of 2,5-bis(2-pivaloyloxymethyl)pyrrole.

One-pot synthesis of 3,4-benzo[c]-β-carbolines was achieved from 2-aryl(tosylamino)methyl-3-bromoindoles via 10 mol % Pd(OAc) 2 /PPh 3 -mediated intramolecular Heck coupling using K 2 CO 3 as a base in DMF at 110 °C with concomitant aromatization through an elimination of tosylsulfinic acid. Under identical conditions, the isomeric 3-aryl(tosylamino)methyl-2bromoindoles upon intramolecular Heck reaction furnished benzo [4,5]isothiazolo[2,3-a]indole 5,5-dioxides instead of the expected γ-carbolines. However, synthesis of the expected γcarboline framework, 3-tosyl-6,9-dihydro-1,2-benzo[a]-γ-carbolines, could be achieved from 3-aryl(tosylamino)methyl-2bromoindoles containing a mesitylene sulfonyl unit as a protecting group on the indole nitrogen.