Brønsted Acid Catalyzed Friedel-Crafts Alkylation of Naphthols with In Situ Generated Naphthol-Derived ortho-Quinone Methides: Synthesis of Chiral and Achiral Xanthene Derivatives

We disclose herein an enantioselective protocol for the Brønsted acid catalyzed addition of naphthols to in situ generated naphthol-derived ortho-quinone methides (o-QMs) followed by intramolecular cyclization, which delivers substituted chiral xanthene derivatives, in a one-pot reaction sequence under mild conditions. This process serves to convert naphthol-derived ortho-hydroxyl benzylic alcohols into reactive naphthol-derived o-QMs using a chiral phosphoric acid (CPA) catalyst. Moreover, it is helpful in controlling the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding followed by intramolecular cyclization. Additionally, for the first time, we observe a Brønsted acid catalyzed C(sp²)-C(sp³) bond cleavage of naphthol-derived ortho-hydroxyl benzylic alcohols for the synthesis of achiral xanthene (sigma plane containing) derivatives in good to excellent yields.

Aromatic or Hetero-aromatic Directly Attached Tri and Tetrasubstituted Methanes: New Chemical Entities as Anti-Infectives

Tri and Tetra-substituted Methanes (TRSMs) are a significant structural motif in many approved drugs and prodrugs. There is increasing use of TRSM units in medicinal chemistry, and many derivatives are specifically designed to make drug-target interactions through new chemical space around TRSM moiety. In this perspective, we describe synthetic challenges for accessing a range of functionalized selective TRSMs and their molecular mechanism of action, especially as anti-infectives. Natural anti-infectives like (+)-Bionectin A, B, (+)-Gliocladine C, Balanocarpol having TRSMs selectively and effectively bind to target proteins in comparison to planar motif having more sp2 carbons perhaps due to conformation which reduces the penalty for conformational entropy with the enhancement of three-dimensionality. Properties of repurposed TRSMs like Almitrine, Ifenprodil, Baricitinib and Remdesivir with their recent progress in COVID-19 therapeutics with their mode of action are also delineated. This perspective is expected to deliver a user guide and reference source for scientists, researchers and academicians in pursuing newly designed TRSMs as therapeutics.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world’s most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage “If you don’t seek, you don’t find”. Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Transition Metal-Catalyzed Cross-Couplings of Benzylic Sulfone Derivatives

In recent years, the use of organosulfones as a new class of cross-coupling partner in transition-metal catalyzed reactions has undergone significant advancement. In this personal account, our recent investigations into desulfonylative cross-coupling reactions of benzylic sulfone derivatives catalyzed by Pd, Ni, and Cu catalysis is described. Combined with the facile α-functionalizations of sulfones, our methods can be used to form valuable multiply-arylated structures such as di-, tri-, and, tetraarylmethanes from readily available substrates. The reactivity of sulfones can be increased by introducing electron-withdrawing substituents such as 3,5-bis(trifluoromethyl)phenyl and trifluoromethyl groups, which enable more challenging cross-coupling reactions. Reactive intermediates including Cu-carbene complexes were identified as key intermediates in sulfone activation, representing new types of C-SO₂ bond activation processes. These results indicate sulfones are powerful functional groups, enabling new catalytic desulfonylative transformations.

Complexation-association-extraction spectrophotometric determination of Pt cations based on a multi-reagent analytical system with I- anions and 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium cations

A new multi-reagent analytical system with 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium chloride (CPVTI), which is a styryl hemicyanine cationic dye with good photostability and a high molar absorption coefficient, as its core is first established and utilized successfully to determine the content of Pt ions via a spectrophotometric method. The process involves two treatment steps: adding CPVTI and I solutions to the Pt solution to be detected, and then using butyl acetate for vortex liquid-liquid extraction. A Pt cation can be incorporated into the CPVTI cation with the help of an I^- anion, initially converting the Pt cation into a [PtI₆]^2- complex anion. After forming a [PtI₆^2-·2CPVTI⁺]_(aq) ion associate in the aqueous phase, the Pt cation can be extracted selectively by butyl acetate with maximum extraction efficiency, and exists as [PtI₆^2-·2CPVTI⁺]_(org) in the extract phase. Via the formation of the iodo-complex of Pt and its ion associate with CPVTI, and the extraction with butyl acetate, Pt is selectively partitioned into the butyl acetate extractant in a step-by-step manner with good interference resistance. In the CPVTI-Pt-I analytical system, the charge state of CPVTI is retained by adjustment with H₂SO₄; the monovalent CPVTI⁺ presents a strong spectrophotometric absorbance signal at 530 nm with long-term stability, which allows determination of the Pt content. The system shows a high molar absorption coefficient of 6.52 × 10⁴ L mol^-1 cm^-1 at 530 nm, a lower limit of detection of 0.07 mg L^-1, and a good Sandell's sensitivity of 0.0030 μg cm^-2. Mechanistic analysis of the establishment of the system, concentration optimization, standard working curve, system sensitivity and stability, resistance against interference from diverse metal ions, and practical applications are investigated and discussed.

NaHSO4/SiO2 catalyzed generation of o-quinone/ o-thioquinone methides: synthesis of arylxanthenes/ arylthioxanthenes via oxa-6π-electrocyclization

ortho-Quinone methides, very reactive transient intermediates, are utilized successfully in synthesizing complex organic molecules of natural and biological significance. Among several synthetic protocols, the acid catalyzed generation of ortho-quinone methides from suitably substituted phenols is a promising method for further exploitation in organic synthesis. Such an interesting reactive species is conveniently employed in the synthesis of conformationally restricted triarylmethane derivatives such as 12/9-arylxanthenes/arylthioxanthenes starting from symmetrical/unsymmetrical 2-(hydroxydiarylmethyl)phenol/thiophenol, respectively, using SiO2-NaHSO4. Conformationally restricted 12/9-arylxanthenes/arylthioxanthenes were obtained in 52 to 96% yields using this protocol, which is believed to involve the formation of o-quinone methides followed by electrocyclic ring closure and isomerization at elevated temperature. Photophysical studies of selected examples in acidic media showed turn-on fluorescence by hydride ion transfer mediated π-conjugated xanthylium salt formation and suggested the application potential in bio-imaging and fluorescent sensors.

Synthesis of Triarylmethanes by Decarbonylation of 3,3-Diaryl Benzofuranones

A simple protocol for the synthesis of triarylmethane derivatives with three different (hetero)aryl groups by decarbonylation of 3,3-diaryl benzofuranones, which can easily be prepared via arylation of benzofuranones, was developed. The reaction proceeds on heating in dimethylformamide (DMF) in the presence of CH₃ONa and water to generate the products in good to excellent yields. This reaction can be easily scaled up to give a triarylmethane in a gram scale. Further chemical manipulation of the products enabled useful transformations of the phenol ring, including reduction, arylation, cyclization, etc.

Metal free highly efficient C–N bond formation through 1,6-addition: synthesis and photophysical studies of diaryl methyl amino acid esters (DMAAEs)

A transition-metal free, proficient strategy for the one-pot synthesis of diverse diaryl methyl amino acid esters (DMAAEs) has been established from the easily accessible chiral amino acid esters and para-quinone methides (QMs) in very good to excellent yields.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.