DFT studies on tautomeric preferences of 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione in the gas phase and in solution

Density functional theory (DFT) calculations show that in vacuum such α-diketone as 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione is much less stable than its enolimine–enaminone ((1Z,3Z)-3-hydroxy-4-(pyridin-2-yl)-1-(quinolin-2(1H)-ylidene)but-3-en-2-one) and dienaminone tautomers ((1Z,3Z)-1-(pyridin-2-yl)-4-(quinolin-2-yl)buta-1,3-diene-2,3-diol). Other its tautomers (multiple basic and acidic centers in their molecules enable multiple proton transfer to take place) are even more labile. Strength of the intramolecular hydrogen bonds and aromatic character of the (quasi)rings [proved by the Harmonic Oscillator Model of Aromaticity (HOMA) index] in their molecules were found to be responsible for the observed tautomeric preferences. Polar and basic solvent disfavors and favors the enolimine and enaminone tautomers, respectively.     

Scrambling of oxygen-18 during the "borderline" solvolysis of 1-(3-nitrophenyl)ethyl tosylate

[reaction: see text] There is substantial isomerization (kiso=0.32 x 10(-3) s(-1)) of 3-NO2C6H4(13)CH(Me)OS(18O)2Tos during solvolysis (ksolv=1.04 x 10(-3) s(-1)) in 50/50 trifluoroethanol/water, even though the estimated lifetime of the putative 1-(3-nitrophenyl)ethyl carbocation intermediate of solvolysis (ca. 10(-13) s(-1)) is too short to allow rearrangement that exchanges the positions of 16O and 18O at the sulfonate leaving group. This suggests that isomerization proceeds by a mechanism that avoids formation of the carbocation-anion pair intermediate.     

Synthesis, Crystal Structure and Theoretical Studies of (E)-1-((9-(2-(2-methoxyethoxy)ethyl)-9H-carbazol-3-yl)methylene)thiosemicarbazide

A novel thiosemicarbazide derivative, (E)-1-(9-(2-(2-methoxyethoxy)ethyl)-9H-carbazol-3-yl) methylene)-thiosemicarbazide (CMT), was synthesized and structurally characterized by IR, 1H-NMR, EI-MS and single-crystal X-ray diffraction. It crystallizes in monoclinic, space group P21/c with a = 14.769(5), b = 8.279(5), c = 17.166(5) , β = 114.391(5)°, V = 1911.6(14) 3, Z = 4, F(000) = 784, Dc = 1.287 g/m3, Mr = 370.47, μ = 0.190 mm-1, the final R = 0.0390 and wR = 0.1358 for 1446 observed reflections with Ⅰ > 2σ(Ⅰ). The UV-vis absorption spectra of CMT were explained based on quantum chemical calculations, using time dependent density functional theory (TD-DFT) at the B3LYP/6-31G (d) level.     

Psilocin analogs. 1. Synthesis of 3-[2-(dialkylamino)ethyl] -and 3-[2-(cycloalkylamino)ethyl] indol-4-ols

The synthesis of four dialkyl and three eyeloalkyl analogs of psilocin (4, R - CH₃), a hallucinogenic principle found in certain fungi, is described. The synthetic route involves four transformations starting with 6,7-dihydroindol-4(5H)one: (1).     

Synthesis and Structure of 5-Aryl-4-[hydroxy(phenyl)methylene]-1-[2-(1H-indol-3-yl)ethyl]pyrrolidine-2,3-diones

Russian Journal of General Chemistry - The reactions of tryptamine with aromatic aldehyde and methyl benzoylpyruvate at room temperature leads to the formation of...     

C(5)H(7)O(2)(+) ions: the correlation between their thermochemistry in acidic solution and their chemistry in the gas phase

Each of a series of C(5)H(6)O(2) isomeric carboxylic acid and unsaturated lactones (1-7) was protonated in both concentrated sulfuric acid and trifluoromethanesulfonic acid. The thermally induced transformations of the protonated species were then studied over a temperature range of -30 to +160 degrees C. In the case of alpha,beta-unsaturated lactones, protonation took place on the carbonyl oxygen and gave the corresponding stable O-protonated species. Conversely, unconjugated lactones and acetylenic acid 7 were converted even at low temperature into the diprotonated ketoacid 8H(2)()o(+2)() by the acid-catalyzed addition of water to the C-protonated precursor. Upon being heated at 160 degrees C, this acid gave protonated 1,3-cyclopentanedione. In the absence of water, decarbonylation followed by polymerization was observed in lactones 4 and 5. The CIMS spectra of compounds 1-7 were recorded using methane, ammonia, and moist air as reagent gases to determine the correlation between the fragmentation routes in the gas phase and the transformations observed in solution. Ammonia and moist air enabled us to determine the different proton affinities of these compounds. The data obtained in strong acids were used to assign reasonable structures to the gas-phase ions.     

Studies on the mechanism of decomposition of 1-methyl-1-(1-naphthyl)ethyl hydroperoxides to 2-(1-naphthyloxy)propenes

Abstract  

Thermal decomposition of 1-methyl-1-(4-methyl-1-naphthyl)ethyl hydroperoxide under gas chromatography-mass spectroscopy (GC–MS) conditions gives 2-((4-methyl-1-naphthyl)oxy)propene as the main product (50.5%), without any detectable traces of the isomeric 2-((5-methyl-1-naphthyl)oxy)propene. This finding excludes the rearrangement pathway of 1-methyl-1-(1-naphthyl)ethyl hydroperoxides to the corresponding 2-(1-naphthyloxy)propenes, which involves formation of a naphthofuran derivative as an intermediate and transfer of the isopropenyloxy group to the 8 position. This result, as well as our previous density functional theory (DFT) calculations, points to the rearrangement pathway involving an oxirane-type intermediate as the most plausible pathway to 2-(1-naphthyloxy)propenes. This rearrangement is responsible for the unusual inhibition effects of 1-methyl-1-(1-naphthyl)ethyl hydroperoxide on the liquid-phase oxidation of isopropylarenes with oxygen.     

Highly linear polyethylenes using the 2-(1-(2,4-dibenzhydrylnaphthylimino)ethyl)-6-(1-(arylimino)ethyl)-pyridylcobalt chlorides: synthesis,characterization and ethylene polymerization

The series of 2-(1-(2,4-dibenzhydrylnaphthylimino)ethyl)-6-(1-(arylimino)ethyl)pyridine derivatives and their cobalt chlorides(Co1.Co5) were synthesized and fully characterized. The representative complexes Co2 and Co3 were confirmed by single crystal X-ray diffraction analyses, indicating pseudo-square-pyramidal geometry around the cobalt centre. All cobalt complexes,activated with either methylaluminoxane(MAO) or modified methylaluminoxane(MMAO), exhibited high activities towards ethylene polymerization, and produced polyethylenes with high molecular weight and highly linear feature as well as unimodal distribution.     

The 2-(diphenylphosphino) ethyl group (DPPE) as a new carboxyl-protecting group in peptide chemistry

The use of the 2-(diphenylphosphino)ethyl group for carboxyl-protection of amino acids or peptides is described. This group is easily introduced by esterification using 2-(diphenylphosphino) ethanol in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. These Dppe esters are stable under the standard conditions for peptide synthesis. Deprotection is carried out under mild conditions by quaternisation using methyl iodide followed by a β-elimination induced by fluoride ion or potassium carbonate.     

A facile route to diastereomeric phosphorus ylides. Chemoselective synthesis of dialkyl (E)-2-[1-(2-oxocyclopentylidene)ethyl]-2-butenedioates

2-Acetylcyclopentanone undergoes a smooth reaction with triphenylphosphine and dialkyl acetylenedicarboxylates to produce dialkyl 2-(1-acetyl-2-oxocyclopentyl)-3-(1,1,1-triphenyl-lambda(5)-phosphanylidene)succinates. These compounds undergo intramolecular Wittig reactions in boiling benzene to produce highly strained spirocyclobutene derivatives, which spontaneously undergo ring-opening reactions to produce dialkyl (E)-2-[1-(2-oxocyclopentyliden)ethyl]-2-butenedioates.     

Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) during thermosensitive phase separation in water

Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMoEoEMa) during thermosensitive phase separation in water have been investigated by infrared spectroscopy. The C=O stretching band can be separated into three components assigned to non-hydrated carbonyl groups and singly and doubly hydrogen-bonded carbonyl groups (1728, 1709, and 1685 cm-1, respectively). Relatively large parts of the carbonyl groups (50% in 30 wt % solution) do not form hydrogen bonds even below the transition temperature (Tp) probably because they possess crowded positions near the backbone. The fraction of hydrogen-bonding carbonyl groups decreased during phase separation by approximately 0.2. Among five nu(C-H) bands, the highest- and the lowest-frequency bands (nu(C-H)A and nu(C-H)E) exhibited relatively large red shifts of 8 and 11 cm(-1), respectively. DFT calculations indicate that the formation of a H-bond between the ether oxygen and water leads to blue shifts of nu(C-H) of adjacent alkyl groups and has a larger effect than a direct H-bond to the alkyl groups, namely, C-H...O H-bonds. The fraction of hydrogen-bonding methoxy oxygens estimated from the position of the nu(C-H)A is 1 at Tp. This result indicates that the methoxy oxygens and the carbonyl are more favorably hydrated than the other at Tp, respectively.     

Reactive intermediates in the reaction of hydrazinecarbothioamides with 2-(bis(methylthio)methylene)malononitrile and ethyl 2-cyano-3,3-bis(methylthio)acrylate

Research on Chemical Intermediates - The reaction of N-substituted hydrazinecarbothioamides with both 2-(bis(methylthio)methylene)malononitrile and ethyl 2-cyano-3,3-bis(methylthio)acrylate...