A C-H oxidation approach for streamlining synthesis of chiral polyoxygenated motifs

Di(hydroperoxy)adamantane adducts: synthesis, characterization and application as oxidizers for the direct esterification of aldehydes

The di(hydroperoxy)adamantane adducts of water (1) and phosphine oxides p-Tol₃PO·(HOO)₂C(C₉H₁₄) (2), o-Tol₃PO·(HOO)₂C(C₉H₁₄) (3), and Cy₃PO·(HOO)₂C(C₉H₁₄) (4), as well as a CH₂Cl₂ adduct of a phosphole oxide dimer (8), have been created and investigated by multinuclear NMR spectroscopy, and by Raman and IR spectroscopy. The single crystal X-ray structures for 1-4 and 8 are reported. The IR and ³¹P NMR data are in accordance with strong hydrogen bonding of the di(hydroperoxy)adamantane adducts. The Raman ν(O-O) stretching bands of 1-4 prove that the peroxo groups are present in the solids. Selected di(hydroperoxy)alkane adducts, in combination with AlCl₃ as catalyst, have been applied for the direct oxidative esterification of n-nonyl aldehyde, benzaldehyde, p-methylbenzaldehyde, p-bromobenzaldehyde, and o-hydroxybenzaldehyde to the corresponding methyl esters. The esterification takes place in an inert atmosphere, under anhydrous and oxygen-free conditions, within a time frame of 45 minutes to 5 hours at room temperature. Hereby, two oxygen atoms per adduct assembly are active with respect to the quantitative transformation of the aldehyde into the ester.

Hydrogen peroxide adducts of triarylphosphine oxides

Five new hydrogen peroxide adducts of phosphine oxides (p-Tol₃PO·H₂O₂)₂ (1), (o-Tol₃PO·H₂O₂)₂ (2), (o-Tol₂PhPO·H₂O₂)₂ (3), (p-Tol₃PO)₂·H₂O₂ (4), and (o-TolPh₂PO)₂·H₂O₂ (5), and the water adduct (o-Tol₂PhPO·H₂O)₂ (6) have been synthesized and fully characterized. Their single crystal X-ray structures have been determined and analyzed. The IR and ³¹P NMR data are in accordance with strong hydrogen bonding of the hydrogen peroxide. The mono- versus dimeric nature of the adduct assemblies has been investigated by DOSY NMR experiments. Raman spectroscopy of the symmetric adducts and the ν(O-O) stretching bands confirm the presence of hydrogen-bonded hydrogen peroxide in the solid materials. The solubilities in organic solvents have been quantified. Due to the high solubilities of 1-6 in organic solvents their ¹⁷O NMR spectra could be recorded in natural abundance, providing well-resolved signals for the P[double bond, length as m-dash]O and O-O groups. The adducts 1-5 have been probed regarding their stability in solution at 105 °C. The decomposition of the adduct 1 takes place by loss of the active oxygen atoms in two steps.

Selective synthesis and stabilization of peroxides via phosphine oxides

MEKPO (methyl ethyl ketone peroxide) and other peroxides can be synthesized selectively and stabilized as hydrogen-bonded phosphine oxide adducts.

The emergence of sulfoxides as efficient ligands in transition metal catalysis

Sulfoxides are capable of forming stable complexes with transition metals and there have been many comprehensive studies into their binding properties. However, the use of sulfoxides, particularly chiral sulfoxides, as ligands in transition metal catalysis is rather less well developed. This review aims to describe these catalytic studies and covers new developments that are showing very promising results and that have led to a renewed interest in this field.

Iron-induced regio- and stereoselective addition of sulfenyl chlorides to alkynes by a radical pathway

The radical addition of the Cl-S σ-bond in sulfenyl chlorides to various C-C triple bonds has been achieved with excellent regio- and stereoselectivity in the presence of a catalytic amount of a common iron salt. The reaction is compatible with a variety of functional groups and can be scaled up to the gram-scale with no loss in yield. As well as terminal alkynes, internal alkynes underwent stereodefined chlorothiolation to provide tetrasubstituted alkynes. Preliminary mechanistic investigations revealed a plausible radical process involving a sulfur-centered radical intermediate via iron-mediated homolysis of the Cl-S bond. The resulting chlorothiolation adducts can be readily transformed to the structurally complex alkenyl sulfides by cross-coupling reactions. The present reaction can also be applied to the complementary synthesis of the potentially useful bis-sulfoxide ligands for transition-metal-catalyzed reactions.

Regio- and stereoselective hydroxylation of 10-undecenoic acid with a light-driven P450 BM3 biocatalyst yielding a valuable synthon for natural product synthesis

We report herein the selective hydroxylation of 10-undecenoic acid with a light-activated hybrid P450 BM3 enzyme. Under previously developed photocatalytic reaction conditions, only a monohydroxylated product is detected by gas chromatography. Hydroxylation occurs exclusively at the allylic position as confirmed from a synthesized authentic standard. Investigation into the stereochemistry of the reaction indicates that the R enantiomer is obtained in 85% ee. The (R)-9-hydroxy-10-undecenoic acid obtained enzymatically is a valuable synthon en route to various natural products further expanding the light-activated P450 BM3 biocatalysis and highlighting the advantages over traditional methods.