Metal-Free, Regioselective, Dehydrogenative Cross-Coupling between Formamides/Aldehydes and Coumarins by C-H Functionalization

Rhodium-catalyzed selenylation and sulfenylation of quinoxalinones 'on water'

A rhodium-catalysed, regioselective synthetic methodology for selenylation and sulfenylation of 3-phenyl quinoxolinones has been developed through N-directed C-H activation in the presence of silver triflimide, and silver carbonate using dichalcogenides 'on water'. The methodology has been proven to be efficient, regioselective and green. Using this method, a range of selenylations and sulfenylations of the substrates has been carried out in good to excellent yields. Further, late-stage functionalisation produced potential anti-tumour, anti-fungal and anti-bacterial agents making these compounds potential drug candidates.

Microwave assisted regioselective halogenation of benzo[b][1,4]oxazin-2-ones via sp2 C-H functionalization

A microwave assisted, palladium-catalyzed regioselective halogenation of 3-phenyl-2H-benzo[b][1,4]oxazin-2-ones has been demonstrated using inexpensive and readily available N-halosuccinimide. The reaction utilizes the nitrogen atom present in the heterocyclic ring as the directing group to afford regioselective halogenated products in good to moderate yields. The established protocol provides wide substrate scope, high functional group tolerance, and high atom and step economy. The reaction proved to be cost-effective and time-saving as it required only a few minutes for completion and is amenable to gram scale. The halogen atoms present in synthesized products provide further scope for post-functionalization. Several post-functionalized products have also been synthesised to demonstrate the high utility of the reaction in the field of drug discovery and late-stage functionalization.

Piperidine-Iodine as Efficient Dual Catalyst for the One-Pot, Three-Component Synthesis of Coumarin-3-Carboxamides

A simple and efficient one-pot, three-component synthetic method for the preparation of coumarin-3-carboxamides was carried out by the reaction of salicylaldehyde, aliphatic primary/secondary amines, and diethylmalonate. The protocol employs piperidine-iodine as a dual system catalyst and ethanol, a green solvent. The main advantages of this approach are that it is a metal-free and clean reaction, has low catalyst loading, and requires no tedious workup.

Dual Role of Oxoaldehydes: Divergent Synthesis of 3-Aryl- and 3-Aroylcoumarins

A facile and efficient synthetic approach to various valuable 3-aryl- and 3-aroylcoumarins by the direct arylation and aroylation of coumarins with glyoxals in a metal-free manner is presented. The aryl glyoxal is for the first time recognized to serve as an aryl surrogate in addition to its role as an aroyl transfer reagent via a simple switch in reaction conditions. The approach accommodates a broad substrate scope and high yields of the two types of cross-coupling reactions starting from identical starting materials.

Sustainable C–H activation approach for palladium-catalyzed, regioselective functionalization of 1-methyl-3-phenyl quinoxaline-2(1H)-ones in water

An environment-friendly approach for regioselective acylation of 1-methyl-3-phenyl quinoxaline-2(1H)-ones was developed using water as a solvent. The protocol exhibits a wide substrate scope and employs commercially available, non-toxic acyl surrogates.

Aldehydes: magnificent acyl equivalents for direct acylation

From the viewpoint of meeting the current green chemistry challenges in chemical synthesis, there is a need to disseminate how the cocktail of acylation and activation can play a pivotal role in affording bioactive acylated products comprising substituted ketone motifs in fewer reaction steps, with higher atom-economy and improved selectivity. In recent years, a significant number of articles employing the title compounds "aldehydes" as magnificent acylation surrogates which are less toxic and widely applicable have been published. This review sheds light on the compounds use for selective acylation of arene, heteroarene and alkyl (sp3, sp2 and sp) C-H bonds by proficient utilization of the C-H activation strategy. Critical insights into selective acylation of diverse moieties for the synthesis of bioactive compounds are presented in this review that will enable academic and industrial researchers to understand the mechanistic aspects involved and fruitfully employ these strategies in designing novel molecules.

Cross-dehydrogenative Coupling Reactions Between Formamidic C(sp2)-H and X-H (X = C, O, N) Bonds

In the last decade, the scientific community has witnessed explosive growth in research on the direct carbamoylation of C-H and X-H (X = N, O) bonds with formamides via cross-dehydrogenative coupling reactions. This novel approach is an effective means of preparing a variety of carboxamide, carbamate as well as urea derivatives, which are prevalent in medicinal chemistry and natural product synthesis. This review elaborates the most important advances and developments in the field, with an emphasis on the reaction patterns and mechanisms.

Chlorophyll-catalyzed photochemical regioselective coumarin C–H arylation with diazonium salts

A metal-free, direct C–H arylation of coumarins with aryl diazonium salts at room temperature using chlorophyll as a green photosensitizer is devised.