Thermal Ring Contraction of Dibenz[b,f]azepin-5-yl Radicals: New Routes to Pyrrolo[3,2,1-jk]carbazoles

Abstract

Flash vacuum pyrolysis (FVP) of N-allyl- or N-benzyldibenz[b,f]azepine at temperatures from 750 to 950 degrees C gives pyrrolo[3,2,1-jk]carbazole as the major product. The mechanism of the ring contraction involves dibenzazepin-1-yl radical formation, followed by transannular attack and formation of a 2-(indol-1-yl)phenyl radical which cyclizes. The mechanism is supported by independent generation of 2-(indol-1-yl)phenyl radicals by two different methods, and the use of 1-(2-nitrophenyl)indole as a radical generator gives an optimized synthetic route to pyrrolo[3,2,1-jk]carbazole (54% overall yield in two steps from indole). The first substituted pyrrolo[3,2,1-jk]carbazoles have been synthesized by FVP methods and also by reactions of the parent compound with electrophiles, leading to a range of 4-substituted pyrrolocarbazoles.

The Production and Characterisation of Novel Conducting Redox‐Active Oligomeric Thin Films From Electrooxidised Indolo[3,2,1‐jk]carbazole

“…However, we have recently shown that flash vacuum pyrolysis (FVP) of 1-(2-nitrophenyl)indole (1) at 875 8C leads to the formation of pyrroloA C H T U N G T R E N N U N G [3,2,1-jk]carbazole (2) via an aryl radical intermediate. [13] Application of this strategy to N-(2-nitrophenyl)carbazole [14] (3) readily gave IC (4) in a yield of 71 % on a gram scale, which is more than adequate for electrochemical film production (Scheme 1). This procedure is one step shorter than the method of Dunlop and Tucker and complements the range of substituted IC derivatives that can be synthesised.…”

“…For reference, a complete 1 H and 13 C NMR analysis of IC was carried out (see the Supporting Information). When IC was prepared by Dunlop and Tucker [12] it was thought that it would be bowl-shaped due to the strain in the central threering system and the preference for nitrogen to adopt a more trigonal pyramidal form.…”

“…General methods: 1 H NMR spectra were recorded on Bruker AVA600 (600 MHz), Bruker DPX360 (360 MHz) or Bruker ARX250 (250 MHz) spectrometers. 13 C NMR spectra were recorded on Bruker DPX360 (91 MHz) or Bruker ARX250 (63 MHz) spectrometers. Chemical shifts (d H and d C ) are quoted in ppm relative to tetramethylsilane.…”

Towards Isocoumarin‐Fused Enediyne Systems through the Electrophilic Cyclization of Methyl o‐(Buta‐1,3‐diynyl)benzoates

“…Solvents were dried under standard conditions. Methyl o-iodobenzoate (1), [32] 2-methyl-6-phenylhexa-3,5-diyn-2-ol (2a), [14a] trimethyl(nona-1,3-diynyl)silane (2c), [33] 6-trimethylsilylhexa-3,5-diyn-1-ol (2d),…”

Synthesis, Structure, and Biological Activities of 10‐Substituted 3,3,6,6‐Tetramethyl‐9‐Aryl‐3,4, 6,7,9,10‐hexahydroacridine‐1,8(2H,5H)‐dione Derivatives

“…They are widely used as anticancer, antibacterial, DNA probe, antitumor, and so on. Therefore, many studies have been carried out on acridinedione derivatives. Tetraketones are extensively used as important precursors for the synthesis of various acridinediones.…”