Flexible Synthesis of Planar Chiral Azoninones and Optically Active Indolizidinones

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.

1,3-Diaza-Claisen Rearrangements of Vinyl Pyrrolidines Tethered to In Situ Generated Carbodiimides Afford Ring-Expanded [9,5]- and [9,6]-Bicyclic Guanidines

Vinyl pyrrolidines tethered to isothioureas are activated to the corresponding carbodiimides with AgOTf and Et₃N. Intramolecular addition of the vinyl pyrrolidine amine to the carbodiimide followed by a 1,3-diaza-Claisen rearrangement affords [9,5]- and [9,6]-bicyclic guanidines depending on the tether length in good to excellent yields. Density functional theory calculations reveal that the pathway involving intramolecular addition of the amine to carbodiimide to afford a zwitterionic intermediate followed by the zwitterionic 1,3-diaza-Claisen rearrangement was consistently a higher energy pathway than the path involving protonation of the zwitterionic intermediate followed by the cationic 1,3-diaza-Claisen rearrangement.

Recent Developments in Transannular Reactions

Transannular reactions have shown a remarkable performance for the construction of polycyclic scaffolds from medium- or large sized cyclic molecules in an unconventional manner. Recent examples of transannular reactions reported from 2011 have been reviewed, emphasizing the excellent performance of this approach when accessing the target compounds. This review also highlights how this methodology provides an alternative approach to other commonly used methodologies for the construction of cyclic entities such as cyclization or cycloaddition reactions