Metal Triflate–Catalyzed Friedel–Crafts Acetylation of 3-Phenylsydnone

Mechanism of Friedel-Crafts Acylation Using Metal Triflate in Deep Eutectic Solvents: An Experimental and Computational Study

In this paper, we develop a method for Friedel-Crafts acylation using metal triflate in deep eutectic solvents. Various metal triflates were tested and provided good to excellent yields of corresponding ketone products. The density functional theory calculation revealed the metal effects on the formation of active intermediate acylium triflate as well as the acidic condition. The metal triflate in the deep eutectic solvent can be recovered and reused with a little loss in the catalytic activity.

Sydnone: Synthesis, Reactivity and Biological Activities

Sydnones are among the most well-known mesoionic compounds. Since their synthesis in 1935 by Earl and Mecknay, numerous researches have shown that the chemical behavior, physical and biological properties of sydnones make them the most useful compounds in organic chemistry. Sydnones undergo thermal 1,3-dipolar cycloaddition reaction with dipolarophiles (alkynes or alkenes) to give exclusively derivatives containing a pyrazole moiety exhibiting numerous applications, such as pharmaceuticals and agrochemicals. However, the sydnone cycloaddition reaction with alkynes requires harsh conditions, like high temperatures and long reaction times, giving poor regioselectivity to the resulting products. To overcome these constraints, new reactions named CuSAC (Copper- Catalyzed Sydnone-Alkyne Cycloaddition) and SPSAC (Strain-Promoted Sydnone- Alkyne Cycloaddition) have been developed, leading to pyrazoles with interesting constant kinetics.

Discovery of Bis-sydnone styryl ketone as a selective cyclooxygenase-2 inhibitor

Background

Various literature sources have documented a wide spectrum of therapeutic properties of sydnones including anti-inflammatory, anticancer, antimicrobial activities. Phenyl styryl ketones and their derivatives as members of the chalcone family have also been reported as significant bioactive molecules. The current study was initiated to evaluate the anti-inflammatory activity of sydnone-based compounds including some novel bis-sydnone styryl ketone hybrids.

Results

Twenty-five sydnone-containing compounds were successfully synthesized. Compounds 46-48 and 56-58 were reported as new sydnone derivatives. Whereas, compounds 61-63 were synthesized as novel molecules containing two sydnone rings linked via α,β-unsaturated ketone. The structures of the synthesized compounds were confirmed by FTIR, 1H NMR, 13C NMR and ToF-MS analyses. The in vitro COX inhibition assay showed varied activity. Compounds 47, 51, 58 and 63 showed the most potent COX inhibitory effects at a concentration of 200 μM. The selectivity index revealed that 63 was the best selective COX-2 inhibitor. Acetylation of the sydnone ring at C-4 was fruitful for the COX inhibitory effects. Docking analysis showed that COX-2 selectivity was due to a favourable positive charged interaction occurring between the sydnone ring of 63 and Arg513 of COX-2. Compound 51 was hydrogen bonded to Arg513. On the other hand, the low inhibitory effect of 63 against COX-1 was due to an unfavourable polar interaction with His513 in the binding pocket of COX-1.

Conclusions

The compounds were successfully synthesized and characterized. Compound 63 had a common architecture and pharmacophoric features with known selective COX-2 inhibitors (the coxib family) which make it a suitable candidate for the designing of selective and safe NSAID.

A Simple, Effective, Green Method for the Regioselective 3-Acylation of Unprotected Indoles

A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)₃ in catalytic amounts is found to be the best catalyst together with the commercially available ionic liquid [BMI]BF₄ (1-butyl-3-methylimidazolium tetrafluoro-borate) as solvent. The reaction is completed in a very short time using monomode microwave irradiation. The catalyst can be reused up to four times without significant loss of activity. A range of substituted indoles are investigated as substrates, and thirteen new compounds have been synthesized.

Crystal structure of 4-(2-bromo-prop-ion-yl)-3-phenyl-sydnone

Sydnones are a class of mesoionic compounds containing a five-membered heterocyclic ring. In general, sydnone com­pounds are synthesized with an aromatic substutuent at the N³ position. This feature, adds to the stability of the heterocyclic ring. In the title compound {systematic name: 4-(2-bromo­propano­yl)-3-phenyl-1,2,3λ⁵-oxa­diazol-3-ylium-5-olate}, C₁₁H₉BrN₂O₃, the aromatic substitutent is an unsubstituted phenyl ring. The sydnone ring is almost planar, with a maximum deviation from the mean plane of 0.023 (1) Å, but is not coplanar with the phenyl ring, having a dihedral angle of 40.93 (8)°. The carbonyl side chain is twisted relative to the syndone ring by 15.8 (2)°. The mol­ecules are packed in the unit cell as pairs related by an inversion center at (1, 0, 1/2). The pairs inter­act via π-stacking, with the distance separating the centroids being 3.824 (1) Å. The Br atom has two contacts, one to an N atom in a neighboring asymmetric unit with a distance of 3.346 (2) Å (the sum of the van der Waals radii is 3.40 Å) and a second to an H atom with a distance of 3.03 Å. The contact with the H atom is perpendicular (C—Br⋯H = 98.60°) to the C—Br bond, and that to the N atom is linear [C—Br⋯N = 169.10 (5)°] to the C—Br bond. The O atom of the sydnone ring is involved in two hydrogen bonds, one intra­molecular with a donor–acceptor distance of 3.1486 (19) Å and a second that is inter­molecular, with a phenyl H atom as the donor and has a donor–acceptor distance of 3.346 (2) Å.