Cyclization products of N-fluorophenyl-β-alanines and their properties

Interaction of 2-and 4-fluorophenylamines with acrylic and itaconic acids leads to the synthesis of the corresponding N-substituted β-alanines, the cyclization of which leads to derivatives of dihydropyrimidinone, 4-carboxy-2-pyrrolidinone, and tetrahydropyridone. Compounds having benzimidazole, pyrazole, and hydrazine fragments in the molecule have been obtained from 4-carboxy-1-(4-fluorophenyl)-2-pyrrolidinone. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 862–869, June, 2006.     

Nucleophilic addition to the tricarbonyl(η-cycloheptadienylium)iron cation by alkoxide ions. Formation of carboalkoxy intermediates

Nucleophilic addition the title compound by alkoxide ions (OR^?) at 0°C proceeds via a red intermediate probably involving metal-nucleophile interaction, and subsequent formation of the carboalkoxy compound C₇H₉Fe(CO)₂(CO₂R). On raising the temperature, the latter compound rearranges spontaneously by a dissociative mechanism to give the corresponding 5-exo-ring compound C₇H₉ORFe(CO)₃.     

FT-IR and FT-raman spectroscopy study of the cyclic anhydride intermediates for esterification of cellulose: I. Formation of anhydrides without a catalyst

In recent years, extensive efforts have been made to find nonformaldehyde durable press finishes to replace the traditional formaldehyde-based reagents for producing wrinkle-free cotton fabrics. 1,2,3,4-butanetetracarboxylic acid (BTCA) has been the most effective nonformaldehyde crosslinking agent. Our previous research has indicated that a polycarboxylic acid esterifies cellulose in two steps: the formation of a 5-membered cyclic anhydride intermediate by the dehydration of two adjacent carboxyl groups, and the reaction between cellulose and the anhydride intermediate to form an ester linkage. In this research, we used Fourier transform infrared and Fourier transform Raman spectroscopy to study the formation of cyclic anhydride intermediates by BTCA and other polycarboxylic acids without the presence of a catalyst. We found that BTCA and other polycarboxylic acids in a crystalline state start to form 5-membered cyclic carboxylic anhydrides when the temperature reaches the vicinity of their melting points with the exception of bifunctional acids, which form cyclic anhydrides at temperatures much higher than their melting points. Intermolecular hydrogen bonding between carboxylic acid groups prevents the formation of the cyclic anhydride intermediates at lower temperatures. We also found that polycarboxylic acids in an amorphous state form cyclic anhydrides at much lower temperatures.     

Aryl cation and carbene intermediates in the photodehalogenation of chlorophenols

The photochemistry of 2,6-dimethyl-4-chlorophenol (6) has been studied in methanol and trifluoroethanol (TFE) through product studies and transient absorption spectroscopy. Chloride loss from triplet 6 gave triplet hydroxyphenyl cation 14, which equilibrated with triplet oxocyclohexadienylydene 15 within a few tens of nanoseconds; the cation can, however, be selectively trapped by allyltrimethylsilane (k(ad) = 10(8)-10(9) m(-1) s(-1)) to give a phenonium ion and the allylated phenol. In neat alcohols, 14 and 15 are reduced through different mechanisms, namely by hydrogen transfer through radical cation 17 and via phenoxyl radical 16, respectively. The mechanistic rationalization has been substantiated by the parallel study of an O-silylated derivative. The work shows that the chemistry of the highly (but selectively) reactive phenyl cation 14 can not only be discriminated from that of the likewise highly reactive carbene 15, but also exploited for synthetically useful reactions, as in this case with alkenes. Photolysis of electron-donating substituted halobenzenes may be the method of choice for the mild generation of some classes of phenyl cations.     

Cyclization of α-terpenols and their acetates by fluorosulfonic acid

It has been shown that the superacid cyclization of α-terpenols and their acetates takes place with structural selectivity and chemo- and stereospecificity and leads to cyclic isoprenoids with higher yields than the cyclization of the corresponding β-terpenols and their acetates.     

Reactions between cellulose diacetate and alkenylsuccinic anhydrides and characterization of the reaction products

Cellulose diacetate (CDA) with degree of substitution (DS) of 2.4 was dissolved in dimethylsulfoxide and reacted with octadecenyl succinic anhydrides (OSAs) using 1-methylimidazole as a promoter. FT-IR and ¹H-NMR analysis of the reaction products revealed that half-esterification occurred on residual hydroxyl groups of CDA by OSA, providing CDA/octadecenyl succinic acid (OSAcid) half esters at yields of more than 90%. The effects of reaction time and temperature on DS of CDA/OSAcid esters were studied in detail. The higher the reaction temperature, the higher the esterification rate to form CDA/OSAcid half esters. The maximum DS values were 0.41 and 0.33 for CDA/n-OSAcid and CDA/i-OSAcid esters, respectively. The original X-ray diffraction pattern of CDA changed with the introduction of OSAcid substituents into CDA, and CDA/OSAcid esters seemed to have thermoplasticity, depending on DS and the chemical structure of the OSAcids. A soil-embedding test of films of CDA and CDA/OSAcid esters indicated that the CDA/OSAcid esters that were prepared maintained the biodegradability of the original CDA.     

Formation of phenoxy and cyclopentadienyl radicals from the gas-phase pyrolysis of phenol

The formation of radicals from the gas-phase pyrolysis of phenol over a temperature range of 400-1000 degrees C was studied using the technique of low temperature matrix isolation electron paramagnetic resonance (LTMI EPR). Cooling the reactor effluent in a CO2 carrier gas to 77 K produces a cryogenic matrix that exhibits complex EPR spectra. However, annealing by slowly raising the matrix temperature yielded well-resolved, identifiable spectra. All annealed spectra over the temperature range of 700-1000 degrees C resulted in the generation of EPR spectra with six lines, hyperfine splitting constant approximately 6.0 G, g = 2.00430, and peak-to-peak width approximately 3 G that was readily assignable, based on comparison with the literature and theoretical calculations, as that of cyclopentadienyl radical. Annihilation procedures along with microwave power saturation experiments helped to clearly identify phenoxy radicals in the same temperature region. Conclusive identifications of cyclopentadienyl and phenoxy radicals were based on pure spectra of these radicals under the same experimental conditions generated from suitable precursors. Cyclopentadienyl is clearly the dominant radical at temperatures above 700 degrees C and is observed at temperatures as low as 400 degrees C. The low-temperature formation is attributed to heterogeneous initiation of phenol decomposition under very low pressure conditions. The high cyclopentadienyl to phenoxy ratio was consistent with the results of reaction kinetic modeling calculations using the CHEMKIN kinetic package and a phenol pyrolysis model adapted from the literature.     

FT-IR and FT-raman spectroscopy study of the cyclic anhydride intermediates for the esterification of cellulose: III. Cyclic anhydrides formed by the isomers of cyclohexanedicarboxylic acid

Multifunctional carboxylic acids have been used as crosslinking agents for cotton and wood pulp cellulose. In our previous research, we found that a polycarboxylic acid esterifies cellulose through the formation of a 5-membered cyclic anhydride intermediate by the dehydration of two carboxyl groups. In this research, we studied the formation of cyclic anhydride intermediates by different isomers of cyclohexanedicarboxylic acid (CHA) so that we can elucidate the effects of molecular structure on the formation of the anhydride intermediates. We found that both cis-and trans-1,2-CHA form 5-membered anhydride intermediates when temperature reaches their melting points and that cis-1,2-CHA forms the cyclic anhydride at temperatures lower than does trans-1,2-CHA. 1,3-CHA forms 6-membered cyclic anhydride at temperatures much higher than its melting point. The formation of a 5-membered cyclic anhydride intermediates takes place at temperatures lower than that of a 6-membered anhydride. This is probably the main reason why those polycarboxylic acids with their carboxylic acid groups bonded to the adjacent carbons of the molecular backbones are more effective crosslinking agents for cellulose than those with their carboxylic groups bonded to the alternative carbons. No formation of cyclic anhydride was found for 1,4-CHA. The formation of a five-membered cyclic anhydride was accelerated by monosodium phosphate, which is used as a catalyst for the esterification of cotton cellulose by polycarboxylic acids.     

Experimental and theoretical study of 2,6-difluorophenylnitrene, its radical cation, and their rearrangement products in argon matrices.

2,6-Difluorophenylnitrene was reinvestigated both experimentally, in Ar matrices at 10 K, and computationally, by DFT and CASSCF/CASPT2 calculations. Almost-pure samples of both neutral rearrangement products (the bicyclic azirine and the cyclic ketenimine) of a phenylnitrene were prepared and characterized for the first time. These samples were then subjected to X-irradiation in the presence of CH2Cl2 as an electron scavenger, which led to ionization of the neutral intermediates. Thereby, it was shown that only the phenylnitrene and the cyclic ketenimine yield stable radical cations, whereas the bicyclic azirine decays to both of these compounds on ionization. The cyclic ketenimine yields a novel aromatic azatropylium-type radical cation. The electronic structure of the title compound is discussed in detail, and its relation to those of the iso-pi-electronic benzyl radical and phenylcarbene is traced.     

Synthesis of poly(spiropyran)s by polycondensation and their photoisomerization behaviors

Poly(spiropyran)s were synthesized by polycondensation of a bis(indoline) monomer with bis(o-positioned formyl and hydroxy)-substituted aromatic monomers in alcoholic solvents. The structures of the products and their molecular weights were determined by the ¹H NMR and GPC measurements, respectively. Furthermore, photoisomerization behaviors of the poly(spiropyran)s were analyzed by the UV–Vis and ¹H NMR measurements of their solutions in dichloromethane upon the UV and visible light irradiations.     

Photocatalytic mineralization of chlorinated organic pollutants in water by polyoxometallates. Determination of intermediates and final degradation products

Homogeneous aqueous solutions of organochlorine pesticides and chlorophenols, namely, lindane, hexachlorobenzene and 2,4-dichlorophenol (2,4DCP), undergo effective photodegradation upon photolysis with UV and near visible light in the presence of a characteristic polyoxometallate catalyst PW₁₂O₄₀ ³⁻. These substrates remained, practically, intact (lindane, HCB) or underwent minor degradation under similar conditions in absence of catalyst. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometallate with H₂O. The system compares with the widely published TiO₂. Chlorohydroquinone (ClHQ), hydroquinone (HQ), chlorobenzoquinone (ClBQ), benzoquinone (BQ), 3,5-dichlorocatechol (3,5DCC) and 4-chlorocatechol (4CC), among others, were identified as the main aromatic intermediates in the photodegradation of 2,4DCP. Acetic acid was detected as ring cleavage product. In all cases the final photodegradation leads to complete mineralization of substrates to CO₂ and HCl.     

N-hydroxypeptides. I. Preparation of N-benzyloxy-α-amino acid anhydrides and their use in peptide synthesis

N-Benzyloxy-DL-α-amino acids are transformed with phosgen to N-benzyloxy-DL-α-amino acid anhydrides which react smoothly with the amino component of peptides to give the corresponding N-benzyloxypeptides.     

Single crystal X-ray structure determinations of the reaction products of cis- and trans-cyclohexanedicarboxylic anhydrides and methylhydrazine

The structures of two of the three isomeric products of the reactions between cis- and trans-cyclohexanedicarboxylic anhydrides and methylhydrazine were determined by single-crystal X-ray methods to ascertain their tautomeric forms and stereochemistries. One product was found to be cis-N-methylamino-1,2-cyclohexanedicarboximide and the other trans-hexahydro-2-methylcyclohexa[d]pyridazine-1,2-dione.