Domino reactions of chromones with activated carbonyl compounds

Domino reactions of chromones with activated carbonyl compounds, such as dimethyl acetone-1,3-dicarboxylate and 1,3-diphenylacetone, and with 1,3-bis(silyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, allow for a convenient synthesis of a great variety of products. The regioselectivity and course of the reaction depends of the substituent located at carbon C3 of the chromone moiety and also on the type of nucleophile employed.

Advances in chromone-based reactants in the ring opening and skeletal reconstruction reaction: access to skeletally diverse salicyloylbenzene/heterocycle derivatives

Salicyloylbenzene/heterocycles are privileged scaffolds found in many natural products and bioactive molecules. Numerous useful approaches for the preparation of these privileged scaffolds have been developed in recent years. Among these approaches, chromone-based reactants have demonstrated their importance in the synthesis of these salicyloylbenzene/heterocycle scaffolds with structural complexity and potential biological appeal. In this review, the recent advances in the synthesis of salicyloylbenzene/heterocycles are summarized and discussed according to the chromone-based reactants which could be achieved in one step via ring-opening and skeletal reconstruction reactions. Both the mechanisms and the applications of the corresponding products in organic and medicinal chemistry are also described.

A facile protocol for the preparation of 2-carboxylated thieno [2,3-b] indoles: a de novo access to alkaloid thienodolin

A metal-free strategy, alternative to the known complex cycloaddition reactions, towards 2-carboxylated thieno [2,3-b] indole derivatives has been successfully developed. The novel approach involves as starting materials easy accessible 1,2-diaza-1,3-dienes and indoline 2-thione and requires mild reaction conditions. Furthermore, the easy work-up required makes this method amenable for a one-pot approach as demonstrated in the preparation of thienodolin, a natural product isolated from Streptomyces albogriseolus that exhibits valuable biological properties.

Regio- and stereoselective synthesis of functionalized and fused heterocycles from Morita-Baylis-Hillman adducts of dicyclopentadienone

An efficient protocol for the Morita-Baylis-Hillman (MBH) reaction of dicyclopentadienone using CTAB has been developed. The MBH adduct was subsequently transformed to its acetate and bromide derivatives. The 1,3-bielectrophilic character of the MBH acetate and bromide was further explored with various 1,3-binucleophiles to construct various oxa-, thia- and aza-heterocycles. These reactions proceed through a cascade double Michael addition of 1,3-binucleophiles to the MBH acetate/bromide under basic conditions. Amenability of these reactions to scale-up and applications of the products in the synthesis of cyclopentenone-fused chromenones and thiopyranoindoles have been demonstrated.

Domino Reactions of Chromones with Heterocyclic Enamines

Domino reactions of heterocyclic enamines with chromone derivatives provides a convenient synthesis of a great variety of annulated heterocyclic ring systems. The course of the reaction depends on the type of substituent located at position 3 of the chromone. Reactions of 3-unsubstituted chromones, 3-nitrochromones, and 3-halochromones proceed by conjugate addition of the carbon atom of the enamine to carbon C-2 of the chromone, ring cleavage, and recyclization via the chromone carbonyl group. In the case of 3-formylchromes, 3-dichloroacetylchromone, 3-perfluoroalkanoylthiochromones, 3-(2-fluorobenzoyl)chromones, and 3-methoxalylchromones the final cyclization proceeds via the carbonyl group located outside the chromone moiety. The functional groups located at the carbonyl group at position 3 of the chromone allow for further synthetic transformations including additional ring closures.

Contents

1 Introduction

2 3-Unsubstituted Chromones

3 3-Nitrochromones

4 3-Formylchromes

5 3-Dichloroacetylchromone

6 3-Perfluoroalkanoylthiochromones

7 3-Methoxalylchromones

8 3-(2-Fluorobenzoyl)chromones

9 3-Halochromones

10 Chromone-3-carboxylic Acids

11 Conclusions

A cascade deprotonation/intramolecular aldol reaction of α-carbonyl sulfonium ylides with 2-mercaptoindole-3-carbaldehydes and 2-mercaptobenzaldehydes to access thieno[2,3-b]indoles and benzothiophenes

The first catalyst-free cascade deprotonation/intramolecular aldol reaction of α-carbonyl sulfonium ylides with 2-mercaptoindole-3-carbaldehydes and 2-mercaptobenzaldehydes was developed. A series of thieno[2,3-b]indoles and benzothiophenes were smoothly obtained in high to excellent yields. The salient features of the protocol include catalyst-free conditions, an environment-friendly solvent, broad substrate scope, and large-scale synthesis.

Synthesis of tetrahydrothiopyrano[2,3-b]indoles via [3+3] annulation of nitroallylic acetates with indoline-2-thiones

[3+3] annulation of 1,3-binucleophilic indolin-2-thione with 1,3-bielectrophilic nitroallylic acetate via an S_N2-reaction-6-endo-trig cyclization takes place with high regio- and stereoselectivity to afford tetrahydrothiopyranoindoles.

PIDA-mediated α-C–H functionalization of enaminones: the synthesis of thiocyano enaminones and chromones in water

Herein, an efficient, metal-free process for the α-C–H thiocyanation of enaminones was developed using PhI(OAc)₂ as an oxidant at room temperature in an aqueous medium.

Synthesis of Functionalized Thieno[2,3-b]indoles via One-Pot Reaction of Indoline-2-thiones with Morita-Baylis-Hillman and Rauhut-Currier Adducts of Nitroalkenes

A straightforward protocol for the synthesis of functionalized thieno[2,3-b]indoles by base-mediated [3 + 2]-annulation of indoline-2-thione with Morita-Baylis-Hillman and Rauhut-Currier adducts of nitroalkenes is described. Complete regioselectivity, broad substrate scope, and mild reaction conditions make this strategy very valuable. Moreover, the thieno[2,3-b]indoles comprising functional groups such as hydrazine and ketoalkyl moieties are amenable for further synthetic elaboration.

A domino reaction of 3-chlorochromones with aminoheterocycles. Synthesis of pyrazolopyridines and benzofuropyridines and their optical and ecto-5′-nucleotidase inhibitory effects

Biologically active fused pyridines were prepared by a new domino reaction.

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

A short and robust approach for the synthesis of 2-(hetero)aryl substituted thieno[2,3-b]indoles from easily available 1-alkylisatins and acetylated (hetero)arenes has been advanced. The two-step procedure includes the “aldol-crotonic” type of condensation of the starting materials, followed by treatment of the intermediate 3-(2-oxo-2-(hetero)arylethylidene)indolin-2-ones with Lawesson’s reagent. The latter process involves two sequential reactions, namely reduction of the C=C ethylidene double bond of the intermediate indolin-2-ones followed by the Paal–Knorr cyclization, thus affording tricyclic thieno[2,3-b]indoles.

Synthesis of substituted pyrroles using a silver-catalysed reaction between isocyanoacetates/benzyl isocyanides and chromones

A novel synthetic strategy to construct substituted-pyrroles has been developed through silver-catalysed cycloadditions of isocyanides with chromones.