Carbazoles palladium-catalyzed synthesis

Sequential amination and C-H activation constitutes the key to a palladium-catalyzed synthesis of carbazoles, which enabled, for instance, efficient assembly of the compound 388 (Equation 111) <2002CC2310>. 

Scheme 28 Palladium-catalyzed synthesis of 7-oxygenated carbazole alkaloids...

Scheme 29 Palladium-catalyzed synthesis of 6-oxygenated carbazole alkaloids and the furo[2,3-c]carbazole alkaloid eustifoline-D (132)...

S. Riedmuller, B.J. Nachtsheim, Palladium-catalyzed synthesis of N-arylated carbazoles using anilines and cyclic diaryHodonium salts, Beil-stein J. Org. Chem. 9 (2013) 1202-1209. 

An efficient synthesis of functionalized carbazoles was developed by the palladium-catalyzed annulation of a variety of internal alkynes. This reaction involves arylpalladation of the alkyne, followed by intramolecular Heck olefination, and double bond isomerization. The iodoindole 588 reacts with the alkyne 589 in the presence of a catalytic amount of palladium(O) to give substituted carbazoles 590. In this reaction two new C-C bonds are formed in a single step. Higher reaction temperatures were necessary due to the low reactivity of the iodoindole (566) (Scheme 5.29). 

Pyrroles, H.M.L. Davies. Synthesis of Porphyrins with Exocy-clic Rings from Cycloalkenopyrroles, T.D. Lash. Palladium-Catalyzed Coupling Reactions of Indoles, A.R. Martin and Q. Zheng. Cycloaddition Reactions of Indole Derivatives, U. Pindur. Transition-Metal Mediated Synthesis of Carbazole Derivatives, H. J. Knoiker. Synthesis of [b]-Annelated Indoles by Thermal Electrocyclic Reactions, S. Hibino and E. Sugi-no. Total Synthesis of (-) and ent (-) Duocarmycin SA, D.L. Boger. Index. I... 

Scheme 15.18 Palladium(ll)-catalyzed synthesis of carbazole-l,4-quinone alkaloids.

Huang, Q., Larock, R. C. Synthesis of Substituted Naphthalenes and Carbazoles by the Palladium-Catalyzed Annulation of Internal Alkynes. J. Org. Chem. 2003, 68, 7342-7349. 

A rather unusual procedure has been published for the palladium- and copper-catalyzed synthesis of triarylamines, using an alkaline water-ethanol emulsion stabilized by cetyltrimethylammonium bromide [41]. Anyway, this method overcomes the problem in the synthesis of N-aryl carbazoles (Eq. 14), which are not accessible by the method developed by Hartwig and Buchwald [42],... 

Much research interest in the synthesis of carbazoles is directed at the preparation of natural products. The total syntheses of murrayafoline A 153 and murrayanine have been reported <04S2499>. The key step included a regioselective cycloaddition between oxazolidinone 150 and acrolein which led to benzoxazol-2-one 151 after DDQ oxidation. Ring opening of the oxazol-2-one ring of 151 followed by methylation provided A-phenylaniline 152. A palladium-catalyzed intramolecular cyclization of the latter then produced the natural product 153. Finally, venerable iron-mediated chemistry has been utilized in the total synthesis of furoclausine A 154 <04SL528> and 6-chlorohyellazole 155 <04SL2705>. 

The aromatic ring version of the Mori-Ban-Heck indole synthesis can be called an aryl-Heck reaction. This palladium-catalyzed cyclization of o-halo diaryl amines has seen many applications in carbazole and carboline synthesis. 

Scheme 2 Knolker Palladium-Catalyzed Carbazole Synthesis...

Quesnel and Arndtsen reported a palladium-catalyzed carbonylation approach to the synthesis of acid chlorides. As an extension of this methodology, it was found that indoles, carbazoles, and anilines could be N-carbonylated at room temperature from simple aryl iodides and carbon monoxide in good yields (229- 230) (13JA16841). 

More recently, a palladium-catalyzed intramolecular C-H arylation with mesylated compounds was reported by Kalyani and co-workers. A sequential mesylation-arylation protocol using phenols as substrates vras described as well. This method allows for the synthesis of diverse heterocyclic motifs, including dibenzofurans, carbazoles, and indoles, in good yields (Scheme 2.30). The intermolecular aiylations were efficient for the coupling of azoles with electronically diverse mesylates. 

In 2013, Takemoto and co-workers developed a palladium-catalyzed isocyanide insertion and alkyne functionalization for the synthesis of 2-arylindole derivatives, including tetracyclic carbazoles (Scheme 2.105). In this process, the formation of two C-C bonds via isocyanide insertion was achieved, and isocyanide was effectively used by incorporating both the C and N atoms as components of the indole skeleton. Regarding the reaction mechanism, the reaction started with the oxidative addition of Pd(0) to aryl... 

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