2H‐[1,3]Oxazino[3,2‐α]indolin‐4(3H)‐ones: A Class Of Polyheterocyclic Indole‐Based Compounds

Abstract

A methodology for the synthesis of 2H‐[1,3]oxazino[3,2‐α]indolin‐4(3H)‐ones is reported. They are obtained from readily available materials by a facile synthetic procedure following either a two‐step cascade reaction or a step‐by‐step transformation. The target compounds represent a hitherto unreported class of indole derivatives with a novel kind of tris‐ or tetracyclic backbone.

Synthesis of N‐Fused Indolines via Copper (II)‐Catalyzed Dearomatizing Cyclization of Indoles

“…Up to this point, some cases involving N ‐tethered indoles are used to synthesize indolines via dearomatizing cyclization (Scheme 1). [10–13] These reactions usually proceed in the presence of a catalyst, such as palladium or nickel salts, or by visible‐light photocatalysis. The dearomative cyclization proceeds with C−C bond formation (Scheme 1, a) [10] .…”

“…The dearomative cyclization proceeds with C−C bond formation (Scheme 1, a) [10] . On the other hand, just recently, our group and others developed protocols for the synthesis of fused indolines by dearomatizing cyclization of N ‐acylindoles [11,12,13] . These reactions involve C−O bond formation in the presence of a palladium catalyst, BBr 3 or triflic acid, and an FeCl 3 catalyst (Scheme 1, b).…”

Synthesis of Polycyclic Indolines by Utilizing a Reduction/Cyclization Cascade Reaction

“…[9,10] To date, the dearomatizing cyclizations of N-substituted indoles to polycyclic indolines has been already developed. [11][12][13][14] E. g., dearomatization proceeds with CÀ C bond formation in the presence of Pd-or Nicatalysts or by visible-light photocatalysis as well as others. [11] Recently, some approaches have been described, which involve CÀ O bond formation in the presence of Pd-catalysts, BBr 3 or triflic acid, and FeCl 3 (Scheme 1a).…”

“…[11] Recently, some approaches have been described, which involve CÀ O bond formation in the presence of Pd-catalysts, BBr 3 or triflic acid, and FeCl 3 (Scheme 1a). [12][13][14] To the best of our knowledge, N-acylindoles with amine or nitro groups as substrates are not systematically studied. Only one approach[a] J.…”

“…Our recent research of the indole dearomatization reaction [13][14] catalyzed by FeCl 3 [15] inspired us to expand the protocol to the direct synthesis of 5a, 6-dihydroindolo[2,1-b] quinazolin-12(5H)-one as basic skeleton by intramolecular nucleophilic attack of an in situ generated non-activated NH 2group to the C2-position of N-acyl indoles. [16] Primary amines (as cyclization precursors) are easily available by reduction of nitro groups using iron metal in the presence of hydrochloric acid.…”