Access to polycyclic carbazoles from ring-fused 2-(9H-carbazol-1-yl)anilines

Abstract

Nine 2-(9H-carbazol-1-yl)anilines with rings fused at the 3,4-position were acylated at the amino group with chloroacetyl, 3-chloropropanoyl, or 4-chlorobutyryl chloride, at yields of 85–99%. The resulting ω-chloroamides were exposed to potassium tert-butoxide in THF. All nine acetamides annulated exclusively at the carbazole N atom, giving benzodiazocinocarbazoles at 76–91% overall yield. The only propanamide prepared underwent α,β-elimination, giving the corresponding acrylamide at 70% overall yield. All nine butanamides annulated exclusively at the amide nitrogen, giving pyrrolidin-2-ones at 70–94% overall yield. Additionally, the 1-indanone derived carbazolylaniline followed the same annulation pattern, but the benzylic methylene group was oxidized, giving the corresponding fluorenones. The cyclohexanone-derived carbazolylaniline was also converted into a maleimide, which participated in a Diels-Alder reaction with cyclopentadiene. Attempts to replace the amino group in the starting material via diazotization were unsuccessful. Instead, a Widman-Stoermer reaction was observed, in which the diazonium group attacked the carbazole 2-position, giving the corresponding cinnoline.

Graphical Abstract

Keywords:

• Acylation
• carbazoles
• intramolecular ring closure
• polycyclics

Additional information

Funding

Supported by the Wayland E. Noland Research Fellowship Fund at the University of Minnesota.