Selectivity Modulation of the Ley–Griffith TPAP Oxidation with N ‐Oxide Salts

Synthesis and structure of clozapine N-oxide hemi(hydro-chloride): an infinite hydrogen-bonded poly[n]catenane

The structure of the title compound, 2C18H19ClN4O·HCl or (CNO)2·HCl (C36H39Cl3N8O2), at 100 K has tetra-gonal (I4/m) symmetry. The dihedral angle between the benzene rings of the fused ring system of the CNO mol-ecule is 40.08 (6)° and the equivalent angle between the seven-membered ring and its pendant N-oxide ring is 31.14 (7)°. The structure contains a very strong, symmetrical O-H⋯O hydrogen bond [O⋯O = 2.434 (2) Å] between two equivalent R 3N+-O- moieties, which share a proton lying on a crystallographic twofold rotation axis. These units then form a (CNO)4·(HCl)2 ring by way of two equivalent N-H⋯Cl hydrogen bonds (Cl- site symmetry m). These rings are catenated into infinite chains propagating along the c-axis direction by way of shape complementarity and directional C-H⋯N and C-H⋯π inter-actions.

Influence of the position of the methyl substituent and N-oxide formation on the geometry and intermolecular interactions of 1-(phenoxyethyl)piperidin-4-ol derivatives

Aminoalkanol derivatives have attracted much interest in the field of medicinal chemistry as part of the search for new anticonvulsant drugs. In order to study the influence of the methyl substituent and N-oxide formation on the geometry of molecules and intermolecular interactions in their crystals, three new examples have been prepared and their crystal structures determined by X-ray diffraction. 1-[(2,6-Dimethylphenoxy)ethyl]piperidin-4-ol, C₁₅H₂₃NO₂, 1, and 1-[(2,3-dimethylphenoxy)ethyl]piperidin-4-ol, C₁₅H₂₃NO₂, 2, crystallize in the orthorhombic system (space groups P2₁2₁2₁ and Pbca, respectively), with one molecule in the asymmetric unit, whereas the N-oxide 1-[(2,3-dimethylphenoxy)ethyl]piperidin-4-ol N-oxide monohydrate, C₁₅H₂₃NO₃·H₂O, 3, crystallizes in the monoclinic space group P2₁/c, with one N-oxide molecule and one water molecule in the asymmetric unit. The geometries of the investigated compounds differ significantly with respect to the conformation of the O-C-C linker, the location of the hydroxy group in the piperidine ring and the nature of the intermolecular interactions, which were investigated by Hirshfeld surface and corresponding fingerprint analyses. The crystal packing of 1 and 2 is dominated by a network of O-H...N hydrogen bonds, while in 3, it is dominated by O-H...O hydrogen bonds and results in the formation of chains.

Determining the necessity of phenyl ring π-character in warfarin

Despite the difficulty in administering a safe dose regimen and reports of emerging resistance, warfarin (1) remains the most widely-used oral anticoagulant for the prevention and treatment of thrombosis in humans globally. Systematic substitution of the warfarin phenyl ring with either 1,3,5,7-cyclooctatetraene (COT) (2), cubane (3), cyclohexane (4) or cyclooctane (5) and subsequent evaluation against the target enzyme, vitamin K epoxide reductase (VKOR), facilitated interrogation of both steric and electronic properties of the phenyl pharmacophore. The tolerance of VKOR to further functional group modification (carboxylate 14, PTAD adduct 15) was also investigated. The results demonstrate the importance of both annulene conferred π-interactions and ring size in the activity of warfarin.

Photocyclization of diarylethenes: the effect of imidazole on the oxidative photodegradation process

It was found that imidazole prevents the side process of diarylethenes photocyclization and the photodegradation of photochromic compounds.

Elucidating the mechanism of the Ley-Griffith (TPAP) alcohol oxidation

The Ley-Griffith reaction is utilized extensively in the selective oxidation of alcohols to aldehydes or ketones. The central catalyst is commercially available tetra-n-propylammonium perruthenate (TPAP, n-Pr₄N[RuO₄]) which is used in combination with the co-oxidant N-methylmorpholine N-oxide (NMO). Although this reaction has been employed for more than 30 years, the mechanism remains unknown. Herein we report a comprehensive study of the oxidation of diphenylmethanol using the Ley-Griffith reagents to show that the rate determining step involves a single alcohol molecule, which is oxidised by a single perruthenate anion; NMO does not appear in rate law. A key finding of this study is that when pure n-Pr₄N[RuO₄] is employed in anhydrous solvent, alcohol oxidation initially proceeds very slowly. After this induction period, water produced by alcohol oxidation leads to partial formation of insoluble RuO₂, which dramatically accelerates catalysis via a heterogeneous process. This is particularly relevant in a synthetic context where catalyst degradation is usually problematic. In this case a small amount of n-Pr₄N[RuO₄] must decompose to RuO₂ to facilitate catalysis.

N-Oxides rescue Ru(v) in catalytic Griffith–Ley (TPAP) alcohol oxidations

Electrochemistry of tetrapropylammonium perruthenate (TPAP) reveals that an unstable Ru(v) complex is reoxidised by amine N-oxides in catalytic Griffith–Ley alcohol oxidations.