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.

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

Arylation of ortho-Hydroxyarylenaminones by Sulfonium Salts and Arenesulfonyl Chlorides: An Access to Isoflavones

Herein we disclose three new methods for the straightforward and efficient synthesis of 3-arylchromones following the arylation of ortho-hydroxyarylenaminones by vast diversities of bench-stable and easy-to-use sulfonium salts and arenesulfonyl chlorides. Both developed methods, namely the light-mediated photoredox and electrophilic arylation, showed good efficiency, and are feasible for the preparation of 3-arylchromones in good-to-excellent yields. This work showcases the first described attempt where the sulfonium salts and arenesulfonyl chlorides were successfully utilized for the construction of the chromone heterocycle system.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.

Synthesis of New Quinolinones from 3-Nitropyranoquinolinones

Alkaline hydrolysis of 3-nitropyranoquinolinones (6-alkyl-4-hydroxy-3-nitro-2 H-pyrano[3,2- c]quinoline-2,5(6 H)-diones) for different reaction times gave five products which were formed by the progressive degradation of the nitropyrano ring. Varying amounts of 3-nitroacetylquinolinones, quinolinones with side-chains of β- and α-ketoacids, quinolinone-3-carboxylic acids and 4-hydroxyquinolinones were isolated. With the aim of preparing new biologically active quinolone derivatives, the products of reaction of the 3-nitropyranoquinolinones with side-chains of β- and α-ketoacids with some nitrogen and carbon nucleophiles were also studied, some giving rise to annulated products.

Synthesis of 4-quinolones, benzopyran derivatives and other fused systems based on the domino ANRORC reactions of (ortho-fluoro)-3-benzoylchromones

This method provides a valuable one-pot shortcut for the synthesis of 4-quinolones, benzopyran derivatives and other fused systems from (ortho-fluoro)-3-benzoylchromones.

One-pot, three-component synthesis of 7-azaindole derivatives from N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds

An efficient and practical route to 7-azaindole framework has been developed by one-pot, three-component cyclocondensation of N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds in ethanol or acetic acid at reflux. Reactions involving tetronic acid, indane-1,3-dione, dimedone, and 5-phenylcyclohexane-1,3-dione gave carbocyclic fused 7-azaindoles, whereas Meldrum's acid, benzoylacetonitrile, and malononitrile resulted in the highly substituted 7-azaindole derivatives, making this strategy very useful in diversity-oriented synthesis (DOS).