Planar Chirality − Synthesis and Transformations of 8- to 10-Membered Heterocycles Bearing (E)-Olefins

Synthesis of novel benzopyrimido[4,5-d]azoninone analogs catalyzed by biosynthesized Ag-TiO2 core/shell magnetic nanocatalyst and assessment of their antioxidant activity

The present work reported the synthesis of novel benzopyrimido[4,5-d]azoninone analogs using a biosynthesized Ag-TiO2 core/shell magnetic nanocatalyst. Accordingly, three-component one-pot reactions of benzoazonine-dione with thiourea and aryl aldehyde derivatives under nanocatalytic and optimized conditions afforded reasonable to brilliant yields of the target products (57-91%). The nanocatalyst was synthesized by a facile method using turmeric ethanol extract as a reducing and chelating agent. The synthesized nanocatalyst was verified by FT-IR, XRD, zeta potential, EDX, SEM, and TEM. The nanocatalyst presented remarkable catalytic activity for the synthesis of the target products. The procedure provided biosynthesis of the nanocatalyst, accessible reagents, high yields and rates of the reactions, nanocatalyst recyclability, and ease of product isolation and purification. The novel products were characterized by FT-IR, 1H-NMR, 13C-NMR, mass spectra, and 2D NMR analysis (COSY, NOESY, HMQC & HSQC) spectral analyses. The antioxidant activity was assessed by DPPH and phosphomolybdate assays, in which the compounds exhibited excellent potency. Overall, this approach could be used to develop new and sustainable methods for the synthesis of antioxidants and other biologically active molecules.

Eight new arnebinol B-based meroterpenoids with planar chirality in the constrained 6/10/5 tricyclic skeleton from Arnebia euchroma and their cytotoxicities

Eight new arnebinol B-based meroterpenoids ((-)-1, 2, 3, (-)-5, and 7-10) with a constrained 6/10/5 tricyclic backbone were isolated from the roots of Arnebia euchroma. The planar and steric structures of these new compounds were unambiguously elucidated by extensive spectroscopic analyses, X-ray diffraction crystallography, and ECD calculations. The predominant relative orientation between H-7 and the Z double bond with a methyl substituent in the rigid 10-membered carbocycle, along with the planar chirality of the Z double bond was analyzed and discussed for the first time. The illustration of the planar chirality derived from the Z double bond should be paid great importance during the structure elucidation on these homologous meroterpenoids. All the isolated meroterpenoids were screened for their cytotoxicities against the HCT-8, PANC-1, HGC-27, HepG2, and PC9 cell lines, and compounds (+)-5 and (-)-5 exhibited the most potent cytotoxicity.

Palladium-Catalyzed [4+4] Cycloadditions for Highly Diastereo- and Enantioselective Synthesis of Functionalized Benzo[b]oxocines

Asymmetric cycloaddition reactions represent a powerful strategy for building up complex molecular architectures, especially those with medium-sized rings. Herein, we disclose a highly diastereo- and enantioselective cycloaddition strategy that involves...

Photoinduced Irreversible Intramolecular Proton Transfer of Arnebinones B, D, and E: The Case of Photoenolization at the p-Benzoquinone-CH2/CH-π System

Arnebinones B, E, and D (1-3) have been found to be sensitive to light, generating complex and diverse proton transfer products when triggered by light. A unique two-step irreversible intramolecular proton transfer of 1 produced five scalemic mixtures, of which four possessed intriguing dual planar chirality. The unprecedented orientation epimerization equilibrium of the intra-annular double bond was first observed and researched in the homologous meroterpenoids by HPLC monitoring and DFT calculations. A "p-benzoquinone-CH₂/CH-π" moiety in the structure was the common key feature for the occurrence of this type of photoenolization reaction. The product transformation processes and universality of this photoinduced irreversible proton transfer reaction were analyzed together with the cytotoxic activities of arnebinones B, D, and E, and their photoreaction products.

Flow Photochemical Syntheses of trans-Cyclooctenes and trans-Cycloheptenes Driven by Metal Complexation

trans-Cyclooctenes and trans-cycloheptenes have long been the subject of physical organic study, but the broader application had been limited by synthetic accessibility. This account describes the development of a general, flow photochemical method for the preparative synthesis of trans-cycloalkene derivatives. Here, photoisom erization takes place in a closed-loop flow reactor where the reaction mixture is continuously cycled through Ag(I) on silica gel. Selective complexation of the trans-isomer by Ag(I) during flow drives an otherwise unfavorable isomeric ratio toward the trans-isomer. Analogous photoreactions under batch-conditions are low yielding, and flow chemistry is necessary in order to obtain trans-cycloalkenes in preparatively useful yields. The applications of the method to bioorthogonal chemistry and stereospecific transannulation chemistry are described.

Stereogenic α-carbons determine the shape and topology of [13]-macrodilactones

The configuration of α-stereogenic centers affects the shape and topology of [13]-macrodilactones. When one α-stereogenic center is substituted, it directs the planar chirality of the macrocycle; when two centers are substituted, both the shape and the topology are influenced.

Synthesis, structure and reactivity of [15]-macrodilactones

Synthesis and characterization of some new [15]-macrodilactones revealed that the interplay between three planar units, a stereogenic center and a hinge atom generated a planar chirality that governs their molecular topology.

Lewis acid catalyzed intramolecular [3 + 2] cross cycloadditions of cobalt-alkynylcyclopropane 1,1-diesters with carbonyls for construction of medium-sized and polycyclic skeletons

A Lewis acid catalyzed intramolecular [3 + 2] cross cycloaddition of cobalt-alkynylcyclopropane 1,1-diesters with carbonyls has been successfully developed. Together with simple and efficient postcycloadditions of the cobalt-alkyne moiety, a general and efficient strategy for construction of structurally complex and diverse medium-sized skeletons and related polycycles was supplied successfully.

Total Synthesis of Hyacinthacine A2: Stereocontrolled 5-aza-cyclooctene Photoisomerization and Transannular Hydroamination with Planar-to-Point Chirality Transfer

The total synthesis of hyacinthacine A2 is reported via a novel transannular hydroamination in which planar chirality of a 5-aza-trans-cyclooctene precursor is transferred to point chirality in the product. Key to the success of this strategy was the development of a method for establishing absolute planar chirality via stereocontrolled photoisomerization of a 5-aza-cis-cyclooctene. This was accomplished by constructing a 5-aza-cis-cyclooctene precursor with a trans-fused acetonide. The improved diastereoselectivity observed upon photoisomerization of this derivative is attributed to the conformational strain of the eight-membered ring in the minor diastereomer.