Intermolecular C-O Addition of Carboxylic Acids to Arynes: Synthesis of o-Hydroxyaryl Ketones, Xanthones, 4-Chromanones, and Flavones

One-pot domino synthesis of five- and six-membered fused dihydropyridines promoted by PPh3-NBS in aqueous medium

A facile one-pot synthesis of five- and six-membered fused dihydropyridines such as chromenodihydropyridines, pyrazolodihydropyridines and isoxazolopyridines was accomplished for the first time by employing PPh₃-NBS via a formal [3 + 2 + 1] cycloaddition of 1,3-bisnucleophiles (i.e., 2-aminochromone, 4-aminochromone, 5-aminopyrazole and 5-aminoisoxazole), β-enaminones and aldehydes in aqueous medium. The present approach involves a Michael type addition followed by intramolecular cyclization leading to the formation of two new C-C bonds and one C-N bond. High compatibility and excellent yields are the advantages of this protocol.

Medicinal chemistry aspects and synthetic strategies of coumarin as aromatase inhibitors: an overview

Coumarin is a bicyclic oxygen bearing heterocyclic scaffold formed by fusion of benzene with the pyrone ring. Because of its unique physicochemical characteristics and the ease with which it may be transformed into a wide range of functionalized coumarins during synthesis, coumarin provides a privileged scaffold for medicinal chemists. As a result, many coumarin derivatives have been developed, synthesized, and evaluated to target a variety of therapeutic domains, thereby making it an attractive template for designing novel anti-breast cancer compounds. The main culprit in estrogen overproduction in the estrogen-dependent breast cancer (EDBC), is the enzyme aromatase (AR), and it is thought to be a significant target for the effective treatment of EDBC. Considering coumarins versatility, this review presents a detailed overview of diverse study of aromatase as a target for coumarins. An overview of structure-activity relationship analysis of coumarin core is also included so as to summarize the desired pharmacophoric features essential for design and development of aromatase inhibitors (AIs) using coumarin core. Identification of key synthesis techniques that could aid researchers in designing and developing novel analogues with significant anti-breast cancer properties along with their mechanism of action have also been covered in the current review.

DBU-Mediated Domino Annulation Reaction of 2-Amino-4H-chromen-4-ones and Aromatic Aldehydes for Synthesis of Polysubstituted 3-Hydroxy-5H-chromeno[2,3-b]pyridinones

A pseudo-three-component annulation reaction of substituted 2-amino-4H-chromen-4-ones with aromatic aldehydes promoted by DBU was investigated to access polysubstituted 5H-chromeno[2,3-b]pyridines. This reaction included a sequential intermolecular nucleophilic addition/Michael cyclization/intramolecular epoxidation/ring opening/aromatization sequence, which possessed excellent step and atom economy in a single operation for generating 3-hydroxy-5H-chromeno[2,3-b]pyridines from readily available substrates.

The Aryne Ene Reaction

Intermolecular aryne ene reactions present opportunities to arylate a wide range of unsaturated substrates in a single step, whilst intramolecular reactions provide expedient access to valuable benzofused carbo- and heterocyclic frameworks. This short review will chart the development of the aryne ene reaction from initial reports that rationalise unexpected byproduct formation in competing [4+2] and [2+2] cycloadditions through to its exploitation in contemporary synthetic methodology.

1 Introduction

2 Alkene Ene Reactions

2.1 Intermolecular

2.2 Intramolecular

3 Alkyne Ene Reactions

3.1 Intermolecular

3.2 Intramolecular

4 Allene Ene Reactions

5 Aromatic Ene Reactions

6 Hetero Ene Reactions

6.1 Enols

6.2 Enamines

6.3 Imines

7 Conclusions

Recent advances in the synthesis of xanthones and azaxanthones

A useful chemical toolbox for (aza)xanthones from 2012 to 2020 that covers the optimization of known procedures and novel methodologies.

Construction of Sulfonyl Dihydrobenzo[c]xanthen-7-ones Core via NH4OAc/PdCl2/CuCl2-Mediated Double Cyclocondensation of α-Sulfonyl o-Hydroxyacetophenones with 2-Allylbenzaldehydes

NH₄OAc/PdCl₂/CuCl₂ mediated domino double cyclocondensation of α-sulfonyl o-hydroxyacetophenones and 2-allylbenzaldehydes provides tetracyclic sulfonyl dihydrobenzo[c]xanthen-7-one core with good to excellent yields in MeOH. The intermediates contain a 3-sulfonyl flavanone motif. Only water is generated as a byproduct. The use of various catalysts and reaction conditions is studied for the facile-operational conversion.

Diversity-Oriented Synthesis of Spiroannulated Benzofuran-3-one Scaffold of Leptosphaerin C and Congeners via Aryne Insertion

A concise synthesis of functionalized cyclohexenone-fused spirobenzofuran-3-ones under mild reaction conditions was developed. The reaction proceeds via insertion of aryne into the C-O bond followed by a regioselective intramolecular conjugate addition. The use of silyl-protected acid was crucial for the transformation. This protocol was successfully applied for the synthesis of leptosphaerin C core and its novel analogues.

Insertion of Arynes into P-O Bonds: One-Step Simultaneous Construction of C-P and C-O Bonds

The insertion of arynes into P-O bonds for the preparation of o-hydroxy-substituted arylphosphine oxides, -phosphinates, and -phosphonates is described. This novel reaction leads to the simultaneous formation of C-P and C-O bonds in one step with good yields and regioselectivities under mild and transition-metal-free conditions. The easy follow-up transformations of the resulting o-hydroxyl group extend these reactions to the facile construction of other ortho-substituted arylphosphorus compounds.

Recent advances of chroman-4-one derivatives: synthetic approaches and bioactivities

Chroman-4-one scaffold is a privileged structure in heterocyclic chemistry and drug discovery. Also, chroman-4-ones are important intermediates and interesting building blocks in organic synthesis and drug design. The structural diversity found in the chroman-4-one family led to their division into several categories including benzylidene-4-chromanones, flavanones (2-phenyl-4-chromanones), isoflavanones (3-phenyl-4-chromanones), spirochromanones, and C-4 modified chroman-4-ones such as hydrazones and oxime derivatives. This review addresses the most significant synthetic methods reported on 4-chromanone-derived compounds and consequently emphasizes on the biological relevance of such compounds.

Interception of benzyne with thioethers: a facile access to sulfur ylides under mild conditions

A fluoride anion kicks off the generation of a high energetic species benzyne, which enables two successive trapping reactions.