Thermal rearrangement of spiro[naphthalene(naphthopyranofurazan)]oxides to spiro[naphthalene(phenalenofurazan)oxides. A probable furazan oxide triggered tandem isomerisation process

Thermal rearrangement of (±)-spiro{naphthalene-1(2H),4′- (naphtho-[2′,1′:2,3]pyrano[4,5-c]furazan)}-2-one-11′-oxides in DMF or acetic anhydride at 140°C gave an isomeric mixture of (±)-spiro{naphthalene-1(2H),1′-(5′-hydroxyphenalene[1,2-c] furazan)}-2-one-2′-oxides and 4′-oxides. The rearranged structure was confirmed from X-ray analysis and was consistent with the through space NOE data. The rearrangement is suggested to be an overall tandem isomerization process. Using variable temperature 1H NMR spectroscopy the lower limit for the isomerisation barrier for a pair of tautomers was calculated to be 22 kcal mol-1 at 423 K. The isomerisation equilibrium for a pair of isomers was studied by variable temperature 1H NMR. The lower limit for the isomerisation barrier was calculated to be 22 kcal mol-1 at 423 K. This low value may be indicative of the difficulty encountered in separating the isomers by chromatography. Semi-empirical AM1 and molecular mechanics calculations suggest that the (±)-spiro{naphthalene-1(2H), 1′-(5′-hydroxyphenalene[1,2-c]furazan)}-2-one-2′-oxides are more stable than their 4′-oxide counterparts, in accordance to the X-ray structure. The lower population of the 4′-oxide isomers relative to that of the 2′-oxide isomers was explained in terms of an unfavourable intramolecular steric interaction found in the low energy structure of the former. © 2005 Elsevier Ltd. All rights reserved

Mono- and Binuclear Copper(I) Complexes of Thionucleotide Analogues and Their Catalytic Activity on the Synthesis of Dihydrofurans

The reaction of copper­(I) halides with 2-thiouracil (TUC), 6-methyl-2-thiouacil (MTUC), and 4-methyl-2-mercaptopyrimidine (MPMTH) in the presence of triphenylphosphine (tpp) in a 1:1:2 molar ratio results in a mixed-ligand copper­(I) complex with the formulas [Cu₂(tpp)₄(TUC)­Cl] (<b>1</b>), [Cu₂(tpp)₄(MTUC)­Cl] (<b>2</b>), [Cu­(tpp)₂(MPMTH)­Cl]·¹/₂CH₃OH (<b>3</b>), [Cu­(tpp)₂(MTUC)­Br] (<b>4</b>), and [Cu­(tpp)₂(MTUC)­I]·¹/₂CH₃CN (<b>5</b>). The complexes have been characterized by FT-IR, ¹H NMR, and UV–vis spectroscopic techniques and single-crystal X-ray crystallography. Complexes <b>1</b> and <b>2</b> are binuclear copper­(I) complexes. Two phosphorus atoms from tpp ligands are coordinated to the copper­(I) ions, forming two units that are linked to each other by a deprotonated TUC or MTUC chelating ligand through a sulfur bridge. A linear Cu–S–Cu moiety is formed. The tetrahedral geometry around the metal centers is completed by the nitrogen-donor atom from the TUC or MTUC ligand for the one unit, while for the other one, it is completed by the chloride anion. Two phosphorus atoms from two tpp ligands, one sulfur atom from MPMTH or MTUC ligand, and one halide anion (Cl, Br, and I) form a tetrahedron around the copper ion in <b>3</b>–<b>5</b> and two polymorphic forms of <b>4</b> (<b>4a</b> and <b>4b</b>). In all of the complexes, either mono- or binuclear intramolecular O–H···X hydrogen bonds enhance the stability of the structures. On the other hand, in almost all cases of mononuclear complexes (with the exception of a symmetry-independent molecule in <b>4a</b>), intermolecular NH···O hydrogen-bonding interactions lead to dimerization. Complexes <b>1</b>–<b>5</b> were studied for their catalytic activity for the intermolecular cycloaddition of iodonium ylides toward dihydrofuran formation by HPLC, ¹H NMR, and LC-HRMS spectroscopic techniques. The results show that the geometry and halogen and ligand types have a strong effect on the catalytic properties of the complexes. The highest yield of dihydrofurans was obtained when “linear” complexes <b>1</b> and <b>2</b> were used as the catalysts. The activity of the metal complexes on the copper­(I)-catalyzed and uncatalyzed intramolecular cycloaddition of iodonium ylide is rationalized through electronic structure calculation methods, and the results are compared with the experimental ones

Comparative Evaluation of Different Targeted and Untargeted Analytical Approaches to Assess Greek Extra Virgin Olive Oil Quality and Authentication

Extra virgin olive oil (EVOO) is a key component of the Mediterranean diet, with several health benefits derived from its consumption. Moreover, due to its eminent market position, EVOO has been thoroughly studied over the last several years, aiming at its authentication, but also to reveal the chemical profile inherent to its beneficial properties. In the present work, a comparative study was conducted to assess Greek EVOOs’ quality and authentication utilizing different analytical approaches, both targeted and untargeted. 173 monovarietal EVOOs from three emblematic Greek cultivars (Koroneiki, Kolovi and Adramytiani), obtained during the harvesting years of 2018–2020, were analyzed and quantified as per their fatty acids methyl esters (FAMEs) composition via the official method (EEC) No 2568/91, as well as their bioactive content through liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) methodology. In addition to FAMEs analysis, EVOO samples were also analyzed via HRMS-untargeted metabolomics and optical spectroscopy techniques (visible absorption, fluorescence and Raman). The data retrieved from all applied techniques were analyzed with Machine Learning methods for the authentication of the EVOOs’ variety. The models’ predictive performance was calculated through test samples, while for further evaluation 30 commercially available EVOO samples were also examined in terms of variety. To the best of our knowledge, this is the first study where different techniques from the fields of standard analysis, spectrometry and optical spectroscopy are applied to the same EVOO samples, providing strong insight into EVOOs chemical profile and a comparative evaluation through the different platforms