Unravelling Lawesson's reagent: the structure of monomeric (4-methoxyphenyl)phosphine disulfide

Lawesson's Reagent: Providing a New Approach to the Forgotten 6-Thioverdazyl Radical

A new method for the preparation of the underrepresented 1,5-dimethyl-6-thioverdazyl radicals has been developed employing Lawesson's reagent (LR). The synthetic route involves the direct thionation of the carbonyl group of the corresponding dialkylbishydrazone followed by cyclization to give the tetrazinanthione verdazyl precursor on a gram scale. Subsequent oxidation yields the 6-thioverdazyl radical. It was determined that thionation of substrates containing electron-withdrawing groups in the ortho- or para-positions was high yielding. In contrast, for the parent phenyl group or substrates bearing weakly electron-donating substituents, thionation efficiency was significantly reduced. This could be overcome by utilizing partial in situ cyclization, which occurs during work up, to generate the tetrazinanthione directly via a one-pot synthesis. Density functional theory suggests that the LR fragment interacts with the carbonyl prior to cycloaddition and subsequent to cycloreversion, leading to the thiocarbonyl. The electronic nature of the radical is characterized with electron paramagnetic resonance as well as the first report of 6-thioverdazyl redox properties.

Determining Ultra-Low Organic Molecular Odor Thresholds in Air Helps Identify the Most Potent Fungal Aroma Compound

The determination of odor threshold values can be performed in various matrices, including air, and serves as a parameter to compare the potencies of odorous compounds. Typically, the odor thresholds in air are determined by gas chromatography-olfactory (GC-O) and referenced to an internal standard, most often (E)-dec-2-enal. Herein, a direct gas chromatography-flame ionization detector-olfactory analysis method for the determination of odor thresholds in air is reported. As model substrates for this novel approach, naturally occurring substances (R)-1-p-menthene-8-thiol as well as (3S,3aS,6R,7aS)-3,6-dimethyl-3a,4,5,6,7,7a-hexahydro-3H-1-benzofuran-2-one were used. The latter compound was synthesized from (-)-isopulegol and exhibited an extremely low odor recognition threshold of 1.9 × 10-6 ng L-1 air, the lowest value reported for a fungal aroma compound thus far.

Towards Symmetric Thioamides: Microwave-Aided Synthesis of Terephthalic Acid Derivatives

The multistep synthesis of novel bis-terephthalthioamides based on methyl esters of amino acids (AAs) was proposed using conventional heating and microwave-assisted approaches. In fact, the comparative case study on the thionation of new symmetrical diamides with Lawesson's reagent (LR) was performed. The microwave-accelerated small-scale methodology was successfully employed on the whole pathway from substrates (Gly, Ala, Val, Tyr, Ser) to products (symmetrical dithioamides of terephthalic acid), resulting in significantly reduced reaction time, energy requirements, and slightly increased reaction yields when compared to conventional heating. Moreover, the intermolecular similarity of novel terephthalic acid derivatives was estimated in the multidimensional space (mDS) of the structure/property-related in silico descriptors using principal component analysis (PCA) and hierarchical clustering analysis (HCA). The distance-oriented structure/property distribution was also correlated with the experimental lipophilic data.

Lewis base-free thiophosphonium ion: a cationic sulfur atom transfer reagent

Phosphorus(v) sulfide and Lawesson's reagent are commonly used thionating reagents which are considered to operate after dissociation into highly reactive dithiophosphorane fragments. We report the synthesis and properties of a monomeric thiophosphonium ion [R2P[double bond, length as m-dash]S]+. The highly electrophilic species reacts with carbonyls in oxo-for-sulfido exchange reactions at room temperature and undergoes phosphorus-chalcogen bond metathesis reactions with phosphine chalcogenides.

Hybridization of Curcumin Analogues with Cinnamic Acid Derivatives as Multi-Target Agents Against Alzheimer's Disease Targets

The synthesis of the new hybrids followed a hybridization with the aid of hydroxy-benzotriazole (HOBT) and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI.HCL) in dry DMF or thionyl chloride between curcumin analogues and cinnamic acid derivatives. IR, 1H-NMR, 13C-NMR, LC/MS ESI+, and elemental analysis were used for the confirmation of the structures of the novel hybrids. The lipophilicity values of compounds were calculated theoretically and experimentally via the reversed chromatography method as RM values. The novel derivatives were studied through in vitro experiments for their activity as antioxidant agents and as inhibitors of lipoxygenase, cyclooxygenase-2, and acetyl-cholinesterase. All the compounds showed satisfying anti-lipid peroxidation activity of linoleic acid induced by 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH). Hybrid 3e was the most significant pleiotropic derivative, followed by 3a. According to the predicted results, all hybrids could be easily transported, diffused, and absorbed through the blood-brain barrier (BBB). They presented good oral bioavailability and very high absorption with the exception of 3h. No inhibition for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 was noticed. According to the Ames test, all the hybrids induced mutagenicity with the exception of 3d. Efforts were conducted a) to correlate the in vitro results with the most important physicochemical properties of the structural components of the molecules and b) to clarify the correlation of actions among them to propose a possible mechanism of action. Docking studies were performed on soybean lipoxygenase (LOX) and showed hydrophobic interactions with amino acids. Docking studies on acetylcholinesterase (AChE) exhibited: (a) hydrophobic interactions with TRP281, LEU282, TYR332, PHE333, and TYR336 and (b) π-stacking interactions with TYR336.

Isolation and Characterization of the Free Phenylphosphinidene Chalcogenides C6 H5 P=O and C6 H5 P=S, the Phosphorous Analogues of Nitrosobenzene and Thionitrosobenzene

The structures and reactivities of organic phosphinidene chalcogenides have been mainly inferred from trapping or complexation experiments. Phosphinidene chalcogenide derivatives appear to be an elusive family of molecules that have been suggested as reactive intermediates in multiple organophosphorus reactions. The quest to isolate "free" phosphinidene chalcogenides remains a challenge in the field. Here, we present the synthesis, IR, and UV/Vis spectroscopic identification of hitherto elusive phenylphosphinidene oxide and phenylphosphinidene sulfide from the corresponding phosphonic diazide precursors. We isolated these higher congeners of nitroso- and thionitrosobenzene in argon matrices at 10 K. The spectral assignments are supported by B3LYP/6-311++G(3df,3pd) and MP2/cc-pVTZ computations.

Photochemical reactions of triplet phenylphosphinidene with carbon monoxide and nitric oxide

Here we report the photochemical reactions of triplet phenylphosphinidene with carbon monoxide and nitric oxide. The photolysis of phenylphosphirane in carbon monoxide-doped matrices enabled the first spectroscopic identification of phenylphosphaketene, the hitherto unreported phosphorus analogue of phenyl isocyanate. The hitherto undisclosed phosphinimine-N-oxyl radical formed upon UV irradiation of the phenylphosphinidene with nitric oxide in argon matrices at 10 K.