Transition-metal-free [3 + 3] annulation of indol-2-ylmethyl carbanions to nitroarenes. A novel synthesis of indolo[3,2-b]quinolines (quindolines)

Abstract

Indol-2-ylmethyl carbanions stabilized by alkoxycarbonyl, cyano or benzenesulfonyl groups react with nitroarenes to form σ H -adducts, which in the presence of base (triethylamine or DBU) and trimethylchlorosilane transform into indolo [3,2-b]quinoline derivatives in moderate to good yields. 194

Intramolecular trapping of an iminium salt: rapid construction of quindoline derivatives

“…Among the numerous known methods, those involving the efficient construction of the pyridine ring have been the focus of considerable attention (Scheme 1a). [38][39][40][41][42][43][44][45] On the basis of a retrosynthetic analysis, we speculated that quindoline scaffolds could be efficiently synthesized by means of pyridine-ring-forming cyclization reactions between diarylamines and a C1 synthon (Scheme 1b).…”