Visible-light-driven site-selective alkylation of the benzo core of coumarins.

An unprecedented, straightforward photochemical platform for efficient site-selective C-H alkylation of the C7 position of the benzocore via the cross coupling between coumarins and NHPI esters, employing Ru(II) as a photocatalyst in visible light, has been reported. Remarkably, this transformation demonstrated broad substrate scope and good functional group compatibility. Controlled experiments and DFT calculations shed some insight into the mechanistic details of the reaction and allowed us to propose a plausible mechanism for the regioselectivity.

Redox activated amines in the organophotoinduced alkylation of coumarins.

The coumarin core represents the quintessential scaffold of many natural products. While C-3 alkylation is easily achievable, effective greener strategies for C-4 alkylation have been less forthcoming. Herein, we report a metal-free photoinduced deaminative strategy for C-4 alkylation of coumarins using redox activated secondary and benzylic amine derived Katritzky pyridinium salts.

Organo Photoinduced Decarboxylative Alkylation of Coumarins with N-(Acyloxy)phthalimide.

A metal-free and mild, photoinduced decarboxylative 4-position alkylation of coumarins has been reported. Photoinduced single electron transfer has been initiated by utilizing the visible-light absorptivity of Eosin Y for a reductive generation of alkyl radicals from N-(acyloxy)phthalimide esters. Depending on the nature of N-(acyloxy)phthalimide esters (primary, secondary, and tertiary carboxylic acid derived), several saturated and unsaturated C-4 alkylated coumarins were synthesized. Both control experiments and photophysical studies supported a radical based mechanism for the selective alkylation.

Pd-Catalyzed regioselective intramolecular dehydrogenative C-5 cross coupling in an N-substituted pyrrole-azole system.

Functionalized polycyclic pyrrole-azole structures possessing fused six membered and seven membered rings were directly synthesized via ligand-enabled, Pd-catalyzed, site selective, intramolecular cross couplings of N-substituted pyrrole-azoles. C5-H activation in the presence of a reactive C2-H remains a challenge that needs to be addressed and this was targeted to be resolved through the present approach by specifically generating the cyclized products with 83-100% selectivity. The featured methodology provides a novel disconnection for the synthesis of pyrrole containing alkaloids and medicinal compounds.

Ligand-promoted intramolecular dehydrogenative cross-coupling using a Cu catalyst: direct access to polycyclic heteroarenes.

A copper(II)-promoted intramolecular C-H coupling reaction between indole-2 and imidazole-2 moieties has been developed for polycyclic heteroarene synthesis. The method provides direct access to biheteroaryl incorporated polycyclic frameworks, which are of huge interest in the area of functional materials and drug-discovery.