Biomimetic Non-Heme Iron-Catalyzed Epoxidation of Challenging Terminal Alkenes Using Aqueous H2O2 as an Environmentally Friendly Oxidant

Catalysis mediated by iron complexes is emerging as an eco-friendly and inexpensive option in comparison to traditional metal catalysis. The epoxidation of alkenes constitutes an attractive application of iron(III) catalysis, in which terminal olefins are challenging substrates. Herein, we describe our study on the design of biomimetic non-heme ligands for the in situ generation of iron(III) complexes and their evaluation as potential catalysts in epoxidation of terminal olefins. Since it is well-known that active sites of oxidases might involve imidazole fragment of histidine, various simple imidazole derivatives (seven compounds) were initially evaluated in order to find the best reaction conditions and to develop, subsequently, more elaborated amino acid-derived peptide-like chiral ligands (10 derivatives) for enantioselective epoxidations

Introduction to stereochemistry & conformational analysis

xv+331hlm.;24c

Theoretical Examination of the S–C–P Anomeric Effect

Three decades after the discovery of a strong S–C–P anomeric effect in 2-diphenylphosphinoyl-1,3-dithiane (<b>1</b>) and 2-trimethylphosphonium-1,3-dithiane (<b>4</b>), its definitive interpretation is still lacking. The present study reports DFT geometry optimizations of <b>1</b>-ax, <b>1</b>-eq, <b>4</b>-ax, and <b>4</b>-eq, which do reproduce the S–C–P anomeric effect in <b>1</b> and <b>4</b>, worth 5.45 and 3.08 kcal/mol, respectively (in chloroform solvent). Weinhold’s NBO analysis supports the existence of dominant n_X → σ*_C–Y stereoelectronic interactions that stabilize the axial conformers

Density Functional Theory Computational Reexamination of the Anomeric Effect in 2‑Methoxy- and 2‑Cyano-1,3-dioxanes and 1,3-Dithianes. Stereoelectronic Interactions Involving the Cyano (CN:) Group Revealed by Natural Bond Orbital (NBO) Analysis

This study reports DFT geometry optimization of the anancomeric (ring conformationally anchored) axial <i>r</i>2-methoxy-<i>trans</i>-4,<i>trans</i>-6-dimethyl- and <i>r</i>-2-cyano-<i>trans</i>-4,<i>trans</i>-6-dimethyl-1,3-dioxanes (<b>1</b>-ax and <b>3</b>-ax, respectively), the equatorial isomers (<b>2</b>-eq and <b>4</b>-eq, respectively), the axial r2-methoxy- and <i>r</i>2-cyano-<i>trans</i>-4,<i>trans</i>-6-dimethyl-1,3-dithianes (<b>5</b>-ax and <b>7</b>-ax, respectively), and the equatorial isomers (<b>6</b>-eq and <b>8</b>-eq, respectively). The computational results reproduce the anomeric effect in <b>1</b>–<b>8</b>, and most importantly, Weinhold’s NBO analysis supports the contribution of n­(X) → σ*­(C–Y) stereoelectronic interactions that stabilize the axial isomers. Furthermore, NBO analysis of delocalization energy <i>E</i>(2) of properly aligned filled/empty orbitals in these isomeric 2-polar-substituted heterocycles reveals that n­(O) → σ*­(C–H_ax) is responsible for the increased charge density at C(2)–H_ax in the equatorial isomers, providing an explanation for the computational observation that very recently led Wiberg, Bailey, Lambert, and Stempel (<i>J. Org. Chem.</i> <b>2018</b>, <i>83</i>, 5242–5255) to discard a potential contribution of n­(X) → σ*­(C–Y) stereoelectronic interactions that stabilize the axial isomers. Interestingly, during the course of this study, two relevant stereoelectronic interactions involving the cyano group were revealed, n­(N) → σ*­(NC–C) and σ­(C(2)–H) → σ*­(C–N)