Synthesis of Thioxanthone 10,10-Dioxides and Sulfone-Fluoresceins via Pd-Catalyzed Sulfonylative Homocoupling

Our report describes the facile and scalable preparation of 9H-thioxanthen-9-one 10,10-dioxides via Pd-catalyzed sulfonylative homocoupling of the appropriately substituted benzophenones. This transformation provides a straightforward route to previously unreported sulfone-fluoresceins and -fluorones. Several examples of these red fluorescent dyes have been prepared, characterized, and evaluated as live-cell permeant labels compatible with super-resolution fluorescence microscopy with 775 nm stimulated emission depletion.

Recent advances in decarbonylative annulation reactions

In recent years, decarbonylative annulation reactions have emerged as one of the most efficient routes to construct a variety of important carbocyclic and heterocyclic scaffolds. The main advantages of this type of reaction are, first, the carbonyl compounds are used as the starting materials which are abundant in nature and second, the major by-product of this reaction is carbon monoxide. In the last two decades, various intramolecular and intermolecular decarbonylative annulation reactions have been performed using carbonyl compounds and alkenes/alkynes/arenes/isocyanates etc. as the annulation partners. These reactions are typically performed either in the presence of or in the absence of a metal catalyst. However, these reactions are still in their infancy as a very little progress has been achieved in these reactions. Through this review article, it is attempted to highlight the recent developments on various decarbonylative annulation reactions which ultimately lead to the formation of important structural moieties.

Recent advances in rhodium-catalyzed C(sp2)-H (hetero)arylation

Arylation is a common behaviour in organic synthesis for the construction of complex structures, especially the biaryls. Among those reported arylation procedures, transition-metal-catalyzed direct C(sp²)-H arylation has been rapidly developed in recent decades and has become a reliable alternative to traditional cross-coupling procedures using organometallic reagents. Great achievements in rhodium-catalyzed C(sp²)-H arylation have been witnessed during the last decade. Aryl halides, simple arenes, aryl boronic acids, arylsilanes, aryl aldehyde, aryl carboxylic acid, diazides, etc. were successfully utilized as arylating reagents under rhodium-catalyzed conditions. In this review, recent achievements in rhodium-catalyzed arylations through C(sp²)-H bond activation were summarized together with the mechanism discussions.

Aerobic Copper-Catalyzed Salicylaldehydic Cformyl -H Arylations with Arylboronic Acids

We report a challenging copper-catalyzed C_formyl -H arylation of salicylaldehydes with arylboronic acids that involves unique salicylaldehydic copper species that differ from reported salicylaldehydic rhodacycles and palladacycles. This protocol has high chemoselectivity for the C_formyl -H bond compared to the phenolic O-H bond involving copper catalysis under high reaction temperatures. This approach is compatible with a wide range of salicylaldehyde and arylboronic acid substrates, including estrone and carbazole derivatives, which leads to the corresponding arylation products. Mechanistic studies show that the 2-hydroxy group of the salicylaldehyde substrate triggers the formation of salicylaldehydic copper complexes through a Cu^I /Cu^II /Cu^III catalytic cycle.

Rh-Catalyzed aldehydic C–H alkynylation and annulation

Novel Rh-catalyzed aldehydic C–H bond alkynylation and annulation for the in situ synthesis of chromones and aurones are described.

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.

N-Heterocyclic Carbene Catalyzed Synthesis of Dihydroxybenzophenones from β-Methylenals and Aurones

N-heterocyclic carbene catalyzed synthesis of 2,2'-dihydroxybenzophenones from β-methylenals and aurones was developed. The cleavage of the C-O bond by a retro-Michael addition is the key step from the spirocyclic intermediate to final product.

Rh-Catalyzed domino synthesis of 4-hydroxy-3-methylcoumarins via branch-selective hydroacylation

A Rh-catalyzed domino synthesis of 4-hydroxy-3-methylcoumarins via branch-selective hydroacylation of acrylates and acrylamides using salicylaldehydes is described.