A Combined Theoretical and Experimental Investigation on the Enantioselective Oxidation of Aryl Benzyl Sulfides in the Presence of a Chiral Titanium Catalyst

Elucidating Sulfide Activation Mode in Metal-Catalyzed Sulfoxidation Reactivity

Interest in the catalytic activation of peroxides, together with the requirement of stereoselectivity for the production of enantiopure sulfoxides, has made sulfoxidation the ideal playground for theoretical and experimental physical organic chemists investigating oxidation reactivity. Efforts have been dedicated for elucidating the catalytic pathway regarding these species and for dissecting out the dominant factors influencing the yield and stereochemistry. In this article, Ti(IV) and Hf(IV) aminotriphenolate complexes have been prepared and investigated as catalysts in the presence of peroxides in sulfide oxidation. Experimental results have been combined with theoretical calculations obtaining detailed mechanistic information on oxygen transfer processes. The study revealed that steric issues are mainly responsible for the formation of intermediates in the oxidation pathway. In particular, we could highlight the occurrence of a blended situation where the steric effects of sulfides, ligands, and oxidants influence the formation of different intermediates and reaction pathways.

Steric issues are mainly responsible for the formation of intermediates in the catalytic activation of the peroxide pathway. In particular, we could highlight the occurrence of a blended situation where the steric effects of sulfides, ligands, and oxidants influence the formation of different intermediates and reaction pathways.

Modern Stereoselective Synthesis of Chiral Sulfinyl Compounds

Chiral sulfinyl compounds, sulfoxides, sulfoximines, sulfinamides, and other derivatives, play an important role in asymmetric synthesis as versatile auxiliaries, ligands, and catalysts. They are also recognized as pharmacophores found in already marketed and well-sold drugs (e.g., esomeprazole) and used in drug design. This review is devoted to the modern methods of preparation of sulfinyl derivatives in enantiopure or enantiomerically enriched form. Selected new approaches leading to racemic products for which the asymmetric variant can be developed in the future are mentioned as well.

Structural insights into methyl- or methoxy-substituted 1-(α-aminobenzyl)-2-naphthol structures: the role of C-H...π interactions

Aminobenzylnaphthols are a class of compounds containing a large aromatic molecular surface which makes them suitable candidates to study the role of C-H...π interactions. We have investigated the effect of methyl or methoxy substituents on the assembling of aromatic units by preparing and determining the crystal structures of (S,S)-1-{(4-methylphenyl)[(1-phenylethyl)amino]methyl}naphthalen-2-ol, C₂₆H₂₅NO, and (S,S)-1-{(4-methoxyphenyl)[(1-phenylethyl)amino]methyl}naphthalen-2-ol, C₂₆H₂₅NO₂. The methyl group influenced the overall crystal packing even if the H atoms of the methyl group did not participate directly either in hydrogen bonding or C-H...π interactions. The introduction of the methoxy moiety caused the formation of new hydrogen bonds, in which the O atom of the methoxy group was directly involved. Moreover, the methoxy group promoted the formation of an interesting C-H...π interaction which altered the orientation of an aromatic unit.

Supramolecular synthons in fluorinated benzyl nitrophenyl sulfides

An entangled gauche-conformation in 4-nitrophenyl pentafluorobenzyl sulfide and its “fingerprint analysis”.

Aluminum derivative peroxides in the (t-BuO)3Al–2t-BuOOH catalytic system as a source of electron-excited dioxygen: a quantum chemical study on a model

The t-BuOOH catalytic decomposition leads to reactive oxygen species including chemically activated and chemically excited (O₂(b¹Σ+g) and O₂(¹Δ_g)) dioxygen.

Enantioselective oxidation of sulfides with H2O2 catalyzed by a pre-formed manganese complex

A facile and environmentally friendly method is presented for the asymmetric oxidation of sulfides with H₂O₂ by an in situ-formed manganese complex, affording the corresponding chiral sulfoxides in high yields and excellent enantioselectivities.

Strong intermolecular exciton couplings in solid-state circular dichroism of aryl benzyl sulfoxides

A series of 13 enantiopure aryl benzyl sulfoxides () with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed.

Aromatic rings in chemical and biological recognition: energetics and structures

This review describes a multidimensional treatment of molecular recognition phenomena involving aromatic rings in chemical and biological systems. It summarizes new results reported since the appearance of an earlier review in 2003 in host-guest chemistry, biological affinity assays and biostructural analysis, data base mining in the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), and advanced computational studies. Topics addressed are arene-arene, perfluoroarene-arene, S⋅⋅⋅aromatic, cation-π, and anion-π interactions, as well as hydrogen bonding to π systems. The generated knowledge benefits, in particular, structure-based hit-to-lead development and lead optimization both in the pharmaceutical and in the crop protection industry. It equally facilitates the development of new advanced materials and supramolecular systems, and should inspire further utilization of interactions with aromatic rings to control the stereochemical outcome of synthetic transformations.

Systematic investigation of CD spectra of aryl benzyl sulfoxides interpreted by means of TDDFT calculations

The CD spectra of 13 crystalline aryl benzyl sulfoxides 1a-m with various substituents on the two aromatic rings were recorded in solution and in the solid state. Solution CD spectra were very homogeneous along the series, consisting in most cases of a couplet-like feature in the 200-300 nm region. The red-shifted component of the couplet, corresponding to the sulfoxide-centered n-pi* transition, is always positive for (R) absolute configuration in accordance with Mislow's rule. The presence of a strong electron-withdrawing substituent on the phenyl ring (nitro or ester group) alters the shape of the CD spectrum. CD calculations using the TDDFT method were run for eight representative compounds using DFT-optimized geometries. In all cases, calculated spectra were in very good agreement with experimental ones and allowed for rationalization of the diverse spectral behaviors. It is demonstrated that TDDFT//DFT calculations represent a reliable option for assigning the absolute configuration of this class of compounds whenever crystals suitable for X-ray are not available. Solid-state CD spectra recorded with the KCl pellet technique were in some cases in agreement with those in solution. However, in other cases new and strong CD signals appeared which were interpreted as being due to intermolecular couplings in the crystals.