Synthesis of functionalized 2-salicyloylfurans, furo[3,2-b]chromen-9-ones and 2-benzoyl-8H-thieno[2,3-b]indoles by one-pot cyclizations of 3-halochromones with β-ketoamides and 1,3-dihydroindole-2-thiones

Abstract

Functionalized 2-salicyloylfurans and 2-benzoyl-8H-thieno[2,3-b]indoles were prepared under mild conditions by reaction of 3-halochromones with β-ketoamides and 1,3-dihydroindole-2-thiones, correspondently. The subsequent oxidative cyclization of the products resulted in formation of the corresponding furo[3,2-b]chromen-9-ones. These molecules could also be directly prepared from 3-halochromones using a one-pot protocol. The cyclization reactions reported herein are mechanistically surprising as they proceed via the oxygen and not via the (more nucleophilic) nitrogen atom of the β-ketoamide.

Construction of Indole‐Fused Heterocycles Starting from 2‐Thioxoindolines, Iminoindolines, and Their Derivatives

“…3-Halochromones 114 bearing electron-donating and naphthyl groups were well tolerated, and the desired products were delivered in reasonable yields. [44] Jha and co-workers developed a base-mediated, one-pot synthesis of [1,3]thiazino[3,2-a]indol-4-ones through a condensation reaction between indoline-2thiones 58 and esters 116 in aqueous medium (Scheme 31a). After screening various solvents, temperature, and bases, the use of KOH as base and H 2 O as solvent was selected as the optimal condition.…”

Domino Reactions of Chromones with Heterocyclic Enamines

“…3-Halogenated chromones represent versatile, readily available building blocks in organic chemistry. 45 The reaction of 3-chlorochromone (90a) with 3-aminopyrazol 13a regioselectively afforded pyrazolo [3,4-b]pyridine 91a in very good yield (Scheme 48). 46 The formation of the product can be explained in analogy to the reaction of 13a with 2,3-unsubstituted chromone (2a) (Scheme 7).…”

A new and convenient synthetic way to 2-substituted thieno[2,3-b]indoles

“…A number of synthetic routes to thieno[2,3- b ]indoles have been described in the literature, including oxidative cyclization of indolin-2-thiones 1 [ 20 ], radical or palladium catalyzed cyclization of 3-(2-bromoindol-3-yl)acrylonitriles 2 [ 21 – 22 ], intramolecular CH/NH-coupling in benzo[ b ]thiophenes 3 [ 23 ], AlCl 3 catalyzed recyclization of 2-(2-isothiocyanatophenyl)furanes 4 [ 24 ], reductive cyclization of 3-(2-nirtophenyl)thiophenes 5 via nitrene intermediates [ 25 – 26 ], and condensation of 3-unsubstituted indolin-2-thione 6 with aliphatic α-bromoaldehydes, α-bromoketones [ 27 ] or 3-halochromones (Hlg = Cl, Br) [ 28 ] under basic conditions ( Scheme 1 ). However, all synthetic methods mentioned above are based on using functionalized indoles, thiophenes, furans or chromone precursors, which require several steps to be prepared.…”