Acid‐Free Synthesis of Carbazoles and Carbazolequinones by Intramolecular Pd‐Catalyzed, Microwave‐Assisted Oxidative Biaryl Coupling Reactions – Efficient Syntheses of Murrayafoline A, 2‐Methoxy‐3‐methylcarbazole, and Glycozolidine

Abstract

A mild and efficient methodology for the synthesis of oxygenated carbazoles from diarylamines under non-acidic conditions was developed, based on a palladium-catalyzed, microwave-assisted double C-H bond activation process. This new protocol was successfully applied to the synthesis of three naturally occurring carbazoles, namely murrayafoline

Iron‐Mediated Total Synthesis of 2,7‐Dioxygenated Carbazole Alkaloids

“…Iron complex salt 6 is easily available on a large scale by the 1‐azadiene‐catalyzed complexation of 1‐methoxycyclohexa‐1,4‐diene ( 8 ) with pentacarbonyliron 20. Aniline 7 is commercially available, but, alternatively, can also be prepared in two steps by O ‐alkylation and hydrogenation from the much cheaper nitrophenol 9 21…”

Palladium‐Catalyzed Oxidative Carbocyclizations

“…In combination with microwave technology, the total synthesis of murrayafoline A and glycozolidine were later developed by MenØndez, [46] employing a similar approach as that used before by Knçlker [47] (Scheme 37). Unfortunately, their approach required very high catalytic loadings of Pd-A C H T U N G T R E N N U N G (OAc) 2 (up to 40 mol %), which makes this process significantly less attractive.…”

Heterocycle Formation via Palladium-Catalyzed C-H Functionalization

“…A variety of naturally occurring electron-rich tricyclic carbazoles could be accessed using this transformation. 14,15 Interestingly Fujii and co-workers were able to design a one-pot procedure for carbazole synthesis by merging anilines and aryl triflates via tandem Buchwald–Hartwig amination/oxidative arylation (Eq. 3).…”