Acid-Catalyzed Decomposition of <i>O</i>‑Silylated α‑Diazo-β-hydroxy Esters: Access to Mixed Monosilyl Acetals

Acid-catalyzed decomposition of diazocarbonyl compounds triggers a wide range of transformations leading to synthetically useful building blocks with high diversity. In this field, the chemistry of α-diazo-β-hydroxy ester substrates is largely dominated by migration processes. We describe herein a new approach to original mixed monosilyl acetals from O-protected α-diazo-β-hydroxy-β-aryl esters and alcohols, catalyzed by trimethylsilyl trifluoromethanesulfonate (TMSOTf). The ratio between these original mixed acetals, the symmetric acetals, and the migration products fluctuates depending on the catalyst, the nature of the alcohols, and the substituent on the aromatic ring. Fifty-six examples are reported herein with yields up to 71% and diastereoselectivity up to 6:1. Such mixed monosilyl acetals constitute a synthetic equivalent of α-substituted β-oxoesters with high potential for further transformations

Enantioselective Ruthenium-Catalyzed 1,3-Dipolar Cycloadditions between <i>C</i>‑Carboalkoxy Ketonitrones and Methacrolein: Solvent Effect on Reaction Selectivity and Its Rational

A catalytic 1,3-dipolar cycloaddition between carboalkoxy ketonitrones and methacrolein under the effect of chiral ruthenium Lewis acid (<i>R</i>,<i>R</i>-<b>1</b>) was developed with high regio-, diastereo-, and enantiocontrol. The diastereochemical outcome of the cycloaddition reaction is marked by a significant solvent effect, and a divergent <i>endo</i> or <i>exo</i> control can be tuned by an appropriate choice of both the solvent and the <i>N</i>- and <i>O</i>-substituents of the ketonitrone. A rationale of the solvent effect, based on the computational study of the interactions between the methacrolein–Ru complex and its counteranion (SbF₆^–), is proposed to explain the selectivities obtained

Chemo‑, Regio‑, and Stereoselective Synthesis of Polysusbtituted Oxazolo[3,2‑<i>d</i>][1,4]oxazepin-5(3<i>H</i>)ones via a Domino oxa-Michael/aza-Michael/Williamson Cycloetherification Sequence

The access to new oxazolo­[3,2-<i>d</i>]­[1,4]­oxazepin-5­(3<i>H</i>)-ones starting from α-bromoamido alcohols and Michael acceptors under mild conditions is presented. This domino process proved to be chemo-, regio-, and stereoselective and allows the formation of a large diversity of highly functional 7-membered rings in good yields up to 95%. The complete shift of the regioselectivity of the intermediate enolate from a C–C to a C–O bond formation, contrary to the already known alkylations of such ambident nucleophiles, is mostly triggered by steric effects. The last step of the sequence was modeled by DFT giving some important insights for this C–C vs C–O bond shift

Synthesis of Oxazolidin-4-ones: Domino <i>O</i>‑Alkylation/Aza-Michael/Intramolecular Retro-Claisen Condensation

An original and rapid domino reaction for access to oxazolidin-4-ones is presented. Simply by heating α-bromoamido alcohol in the presence of KNaCO₃ and water with readily prepared Michael acceptors, an unprecedented molecular rearrangement is generated. This new methodology enables the hitherto unreported synthesis of functionalized oxazolidin-4-ones. The process was proved to be compatible with a wide variety of substrates, and high regioselectivities were achieved

Evidence of New Fluorinated Coordination Compounds in the Composition Space Diagram of FeF₃/ZnF₂–H<i>amtetraz</i>-HF_aq System

The exploration of the composition space diagram of the FeF₃/ZnF₂–H<i>amtetraz</i>-HF_aq system (H<i>amtetraz</i> = 5-aminotetrazole) by solvothermal synthesis at 160 °C for 72 h in dimethylformamide (DMF) has evidenced five new hybrid fluorides (<b>1</b>–<b>5</b>); the structures are characterized from single crystal X-ray diffraction data. [H<i>dma</i>]­·(ZnFe^III(H₂O)₄F₆) (<b>1</b>) and [H<i>dma</i>]­·[H<i>gua</i>]₂­·(Fe^IIIF₆) (<b>2</b>) contain anionic inorganic chains (<b>1</b>) or isolated octahedra (<b>2</b>) weakly hydrogen bonded (Class I hybrids) to dimethylammonium (H<i>dma</i>) and/or guanidinium (H<i>gua</i>) cations which are produced from the tetrazole ligand and solvent decomposition. [H<i>dma</i>]₂­·[H<i>gua</i>]­·[NH₄]­·[ZnFe^IIIF₅(<i>amtetraz</i>)₂]₂ (<b>3</b>), [H<i>dma</i>]₂­·[Zn_1.6Fe^II_0.4Fe^IIIF₆­(<i>amtetraz</i>)₃] (<b>4</b>), and [H<i>dma</i>]­·[Zn₄F₅(<i>amtetraz</i>)₄] (<b>5</b>) are considered as Class II hybrids in which the (<i>amtetraz</i>)⁻ anions are strongly linked to divalent metal cations via N–M bonds. In <b>3</b>, _∞{[NH₄]­·[ZnFe^IIIF₅­(<i>amtetraz</i>)₂]₂} layers are separated by [H<i>dma</i>]⁺ and [H<i>gua</i>]⁺ cations. <b>4</b> and <b>5</b> exhibit three-dimensional (3D) hybrid networks that contain small cavities where [H<i>dma</i>]⁺ cations are inserted. A porous 3D metal–organic framework intermediate is evidenced from the thermogravimetric analysis and X-ray thermodiffraction of <b>5</b>