Asymmetric Syntheses of 1-Deoxy-6,8a-di-epi-castanospermine and 1-Deoxy-6-epi-castanospermine

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.

Transannular Approach to 2,3-Dihydropyrrolo[1,2-b]isoquinolin-5(1H)-ones through Brønsted Acid-Catalyzed Amidohalogenation

A transannular approach has been developed for the construction of pyrrolo[1,2-b]isoquinolinones starting from benzo-fused nine-membered enelactams. This process takes place in the presence of a halogenating agent and under Brønsted acid catalysis and proceeds via a transannular amidohalogenation, followed by elimination. The reaction has been found to be wide in scope, enabling the formation of a variety of tricyclic products in good overall yield, regardless of the substitution pattern in the initial lactam substrate. The reaction has also been applied to the total synthesis of a reported topoisomerase I inhibitor and to the formal synthesis of rosettacin. Further extension of this methodology allows the preparation of 10-iodopyrrolo[1,2-b]isoquinolinones by using an excess of halogenating agent and these compounds can be further manipulated through standard Suzuki coupling chemistry into a variety of 10-aryl-substituted pyrrolo[1,2-b]isoquinolinones.

[3,3] Ring Rearrangement of Oxo- or Aza-Bridged Bicyclo[3.2.1]octene-Based 1,5-Dienes

We report that oxo- or aza-bridged alkylidenemalononitrile-cycloheptenes undergo a [3,3] ring rearrangement to yield cyclopenta-fused dihydro-furans or pyrroles. Described herein are the origins of the serendipitous discovery, scope studies, and representative functional group interconversion chemistry.

Asymmetric Synthesis of (-)-6-Desmethyl-Fluvirucinine A₁ via Conformationally-Controlled Diastereoselective Lactam-Ring Expansions

The versatile synthesis of (−)-6-desmethyl-fluvirucinine A₁ was accomplished at a 24% overall yield through a thirteen-step process from a known vinylpiperidine. The key part involved the elaboration of the distal stereocenters and a macrolactam skeleton via conformationally-induced diastereocontrol and the iterative aza-Claisen rearrangements of lactam precursors.

Construction of the Azacyclic Core of Tabernaemontanine-Related Alkaloids via Tandem Reformatsky-Aza-Claisen Rearrangement

A divergent synthetic methodology for a tabernaemontanine-related alkaloid was developed. The synthetic route features practical improvements in the Pictet-Spengler cyclization for the tetrahydro-β-carboline intermediate and an unprecedented tandem Reformatsky-aza-Claisen rearrangement to create the core carbon skeleton and stereochemistries of tabernaemontanine-related alkaloids.

Recent Advances in Substrate-Controlled Asymmetric Induction Derived from Chiral Pool α-Amino Acids for Natural Product Synthesis

Chiral pool α-amino acids have been used as powerful tools for the total synthesis of structurally diverse natural products. Some common naturally occurring α-amino acids are readily available in both enantiomerically pure forms. The applications of the chiral pool in asymmetric synthesis can be categorized prudently as chiral sources, devices, and inducers. This review specifically examines recent advances in substrate-controlled asymmetric reactions induced by the chirality of α-amino acid templates in natural product synthesis research and related areas.

Enantioselective synthesis of polyhydroxyindolizidinone and quinolizidinone derivatives from a common precursor

A concise asymmetric synthetic route to two new tetrahydroxyindolizidinone and quinolizidinone derivatives has been developed from a common intermediate which featured a highly selective dihydroxylation reaction and a RCM reaction as key steps.

Divergent total synthesis of 1,6,8a-tri-epi-castanospermine and 1-deoxy-6,8a-di-epi-castanospermine from substituted azetidin-2-one (β-lactam), involving a cascade sequence of reactions as a key step

A divergent, short, and novel total synthesis of 1,6,8a-tri-epi-castanospermine (7) and 1-deoxy-6,8a-di-epi-castanospermine (8) has been developed via a common precursor, 15, obtained from D-mannitol derived β-lactam. The key step involves a one pot cascade sequence of trimethyl sulfoxonium ylide based cyclization of epoxy sulfonamide 14via epoxide ring opening, one carbon homologation followed by intramolecular cyclization.

Metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization: stereospecific construction with concomitant functionalization of indolizin-5(1H)-one

A metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization strategy has been developed for the stereospecific construction with concomitant derivation of biologically significant indolizin-5(1H)-ones from simple and commercial starting materials. The transformations are notable because they can yield five new σ bonds and six stereocenters including a quaternary carbon center in a single operation.