Intramolecular Direct Arylation of 3-Halo-2-pyrones and 2-Coumarins

Synthesis of tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles via palladium-catalyzed intramolecular direct heteroarylation

We report a palladium-catalyzed intramolecular direct heteroarylation of oxazole tethered β-naphthols to access corresponding tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles. Various functional groups are well tolerated and furnished the desired products in good to excellent yields under the present reaction conditions. The scale-up reaction and synthetic utility of the resulting molecules have been demonstrated. Moreover, UV/vis absorption and fluorescence emission properties have been evaluated for these polyheterocyclic compounds.

Synthesis of Phenolic Coumestans via a Sequential Dehydrogenation/Oxa-Michael Addition Reaction of 2',4'-Dihydroxyl-3-arylcoumarins

A facile and practical approach for the synthesis of natural coumestans and derivatives starting from 2',4'-dihydroxyl-3-arylcoumarins has been developed. The process involved a seqential intramolecular dehydrogenation/oxa-Micheal reaction efficiently promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene at 40 °C under metal- and ligand-free conditions with good functional group compatibility.

Transition metal-catalyzed coupling of heterocyclic alkenes via C–H functionalization: recent trends and applications

Heterocyclic alkenes and their derivatives are an important class of reactive feedstock and valuable synthons. This review highlights the transition-metal-catalyzed coupling of heterocyclic alkenes via a C–H functionalization strategy.

Copper-catalyzed intramolecular cross dehydrogenative coupling approach to coumestans from 2'-hydroxyl-3-arylcoumarins

A copper-catalyzed intramolecular cross dehydrogenative C-O coupling reaction of 2'-hydroxyl-3-arylcoumarins was developed. This protocol provided a facile and efficient strategy for the construction of natural coumestans and derivatives in moderate to high yields. This transformation exhibited good functional group compatibility and was amenable to substrates with free phenolic hydroxyl groups.

Pd(ii)/Ag(i)-Cocatalyzed ortho direct arylation of O-phenylcarbamates with pinacol aryl boronates

Ortho direct arylation of O-phenyl carbamates using aryl boronates as coupling partners has been realized for the first time using Pd(OAc)₂ and AgOAc as co-catalyst.

One-pot two-step synthesis of 3-iodo-4-aryloxy coumarins and their Pd/C-catalyzed annulation to coumestans

An efficient protocol for the synthesis of various coumestans from the intramolecular annulation of 3-iodo-4-aryloxy coumarins through C–H activation has been developed.

A Novel Non-Peptidic Agonist of the Ghrelin Receptor with Orexigenic Activity In vivo

Loss of appetite in the medically ill and ageing populations is a major health problem and a significant symptom in cachexia syndromes, which is the loss of muscle and fat mass. Ghrelin is a gut-derived hormone which can stimulate appetite. Herein we describe a novel, simple, non-peptidic, 2-pyridone which acts as a selective agonist for the ghrelin receptor (GHS-R1a). The small 2-pyridone demonstrated clear agonistic activity in both transfected human cells and mouse hypothalamic cells with endogenous GHS-R1a receptor expression. In vivo tests with the hit compound showed significant increased food intake following peripheral administration, which highlights the potent orexigenic effect of this novel GHS-R1a receptor ligand.

Syntheses of pterocarpenes and coumestans via regioselective cyclodehydration

A highly efficient synthetic route to pterocarpenes and coumestans is described. BCl3-mediated dehydrative cyclization of 1,3-diaryloxyacetones under mild conditions permitted regioselective ring closure to afford 3-((2-iodoaryloxy)methyl)benzofurans which were converted to the corresponding pterocarpenes by Pd-catalyzed intramolecular direct arylation. The subsequent benzylic oxidation led to coumestans. This sequence was applied to the formal syntheses of coumestrol and the proposed structure of plicadin as well as total syntheses of flemichapparins B and C.

Intramolecular cross dehydrogenative coupling of 4-substituted coumarins: rapid and efficient access to coumestans and indole[3,2-c]coumarins

A palladium-catalyzed highly efficient and atom-economical intramolecular cross dehydrogenative coupling (CDC) reaction to access fused polyheterocycles containing a coumarin nucleus has been developed.

Palladium(ii) oxide impregnated on magnetite as a catalyst for the synthesis of 4-arylcoumarins via a Heck-arylation/cyclization process

Heck-arylation/cyclization was achieved using heterogeneous palladium(ii) oxide impregnated on magnetite catalyst (2.5 mol%) with a lower catalyst loading than that reported for similar processes.

Competing amination and C–H arylation pathways in Pd/xantphos-catalyzed transformations of binaphthyl triflates: switchable routes to chiral amines and helicene derivatives

A Pd(OAc)₂/xantphos catalyst system can be tuned to promote either amination or C–H arylation of hindered binaphthyl 2-triflates, with xantphos's hemilability playing a key role.