Room-Temperature, Copper-Free, and Amine-Free Sonogashira Reaction in a Green Solvent: Synthesis of Tetraalkynylated Anthracenes and In Vitro Assessment of Their Cytotoxic Potentials

The multifold Sonogashira coupling of a class of aryl halides with arylacetylene in the presence of an equivalent of Cs₂CO₃ has been accomplished using a combination of Pd(CH₃CN)₂Cl₂ (0.5 mol %) and cataCXium A (1 mol %) under copper-free and amine-free conditions in a readily available green solvent at room temperature. The protocol was used to transform several aryl halides and alkynes to the corresponding coupled products in good to excellent yields. The rate-determining step is likely to involve the oxidative addition of Ar-X. The green protocol provides access to various valuable polycyclic aromatic hydrocarbons (PAHs) with exciting photophysical properties. Among them, six tetraalkynylated anthracenes have been tested for their anticancer properties on the human triple-negative breast cancer (TNBC) cell line MDA-MB-231 and human dermal fibroblasts (HDFs). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to find out the IC₅₀ concentration and lethal dose. The compounds being intrinsically fluorescent, their cellular localization was checked by live cell fluorescence imaging. 4',6-Diamidino-2-phenylindole (DAPI) and propidium iodide (PI) staining was performed to check apoptosis and necrosis, respectively. All of these studies have shown that anthracene and its derivatives can induce cell death via DNA damage and apoptosis.

Pd-Catalyzed decarboxylative alkynylation of alkynyl carboxylic acids with arylsulfonyl hydrazides via a desulfinative process

The decarboxylative alkynylation of alkynyl carboxylic acids and arylsulfonyl hydrazides by desulfinative coupling could provide aryl alkynes in satisfactory yields by either judiciously selecting palladium catalysts or modulating phosphine ligands under mild conditions.

Palladium(II)-Catalyzed Deacylative Allylic C-H Alkylation

The first deacylative allylic C-H alkylation has been established by employing the palladium-catalyzed allylic C-H activation and decarboxylative nucleophile generation. A wide scope of nucleophiles are tolerated and densely functionalized alkylation products turn out to be furnished in moderate to good yield. More importantly, this strategy provides an alternative method for the allylic C-H alkylation with less stabilized carbon nucleophiles, and can be further expanded to the synthesis of unconjugated enynes.