Aromatic Annelation. II. Synthesis of phenols.

The preparation of substituted phenols from cycloalkanones by elaboration of an aromatic ring is described.     

Evaluation of a Combined Quantum Chemical Method Used in Calculating O?H Bond Dissociation Enthalpy

O? H bond dissociation enthalpies (BDE) for a variety of substituted phenols were calculated using a combined quantum chemical method. It is found that the calculated O? H BDE correlated well with the recommended values, except for ortho‐tert‐butyl substituted phenols. For the electron‐donating group substituted phenols the calculated O? H BDE are slightly higher than the recommended values, however, for the electron‐withdrawing group substituted phenols the calculated O? H BDE are slightly lower than the recommended values.     

Correlation of the acidity of substituted phenols,anilines, and benzoic acids calculated by MNDO,AM1, and PM3 with Hammett-type substituent constants

Heats of formation and net atomic charges of some 120 structures involving substituted phenols, anilines, and benzoic acids and the corresponding anions were calculated by MNDO, AM1, and PM3 semiempirical methods. The gas phase acidities of substituted phenols and anilines and the net atomic charges on the anionic heteroatoms of the corresponding anions have been successfully correlated with σ^? constants. Moreover, good correlations with σ were found for the charges on the acidic hydrogens of substituted phenols and anilines. In contrast, the gas phase acidities of substituted benzoic acids and the charges on the anionic oxygens of the corresponding anions are better correlated with Taft σ° constants. Comparisons of these results with experimental data and ab initio theoretical calculations indicate that AM1 and PM3 methods are much better than MNDO in predicting the acidity of aromatic compounds.     

How H-bonding affects aromaticity of the ring in variously substituted phenol complexes with bases. 4. Molecular geometry as a source of chemical information

Aromaticity of the ring of variously substituted phenols in their H-bonded complexes with various bases was a subject of analysis based on 664 geometries retrieved from CSD and by use of the aromaticity index HOMA. GEO and EN, the components of the HOMA index, describing a decrease of aromaticity due to an increase of bond alternation (GEO term) and bond elongation (EN term), were also studied. There is an approximate monotonic dependence of HOMA and GEO on the H-bond strength estimated by the C-O bond length of the hydroxyl group in phenols.     

CuI/Oxalamide Catalyzed Couplings of (Hetero)aryl Chlorides and Phenols for Diaryl Ether Formation

Couplings between (hetero)aryl chlorides and phenols can be effectively promoted by CuI in combination with an N‐aryl‐N′‐alkyl‐substituted oxalamide ligand to proceed smoothly at 120 °C. For this process, N‐aryl‐N′‐alkyl‐substituted oxalamides are more effective ligands than bis(N‐aryl)‐substituted oxalamides. A wide range of electron‐rich and electron‐poor aryl and heteroaryl chlorides gave the corresponding coupling products in good yields. Satisfactory conversions were achieved with electron‐rich phenols as well as a limited range of electron‐poor phenols. Catalyst and ligand loadings as low as 1.5 mol % are sufficient for the scaled‐up variants of some of these reactions.     

Cyclopolymerization. VI. Preparation and Properties of Crosslinked Polyamines by Cyclopolymerization

Crosslinked polymer and copolymers containing tertiary amino groups were prepared from a number of allylamino monomers by cyclopolymerization. The effects of the initiator residue, reaction conditions, monomer structure, and degree of crosslinking on specific properties such as ion-exchange capacity, pKa, and range of nitrogen basicities were investigated.     

Synthesis of substituted benzenes and phenols by ring-closing olefin metathesis

New synthetic approaches to substituted aromatic compounds are reported. Ring-closing olefin metathesis (RCM)/dehydration and RCM/tautomerization are the key processes in the synthesis of substituted benzenes 3 and phenols 6, respectively. Readily accessible 1,5,7-trien-4-ols 7, which are the precursors of benzenes, were prepared from beta-halo-alpha,beta-unsaturated aldehydes 11 or beta-halo-alpha,beta-unsaturated esters 19 by utilizing reliable transformations in which cross-coupling with vinylic metal reagents 12 and allylation with allylic metal reagents 13 were employed as carbon-carbon bond forming reactions. RCM of 7, followed by dehydration, afforded a wide variety of substituted benzenes 3. In addition, RCM of 1,5,7-trien-4-ones 9, which were prepared by oxidation of 7, furnished various substituted phenols 6 by automatic tautomerization.     

The effect of ring nitrogen atoms on the homolytic reactivity of phenolic compounds: understanding the radical-scavenging ability of 5-pyrimidinols

Six substituted 5-pyrimidinols were synthesized, and the thermochemistry and kinetics of their reactions with free radicals were studied and compared to those of equivalently substituted phenols. To assess their potential as hydrogen-atom donors to free radicals, we measured their O-H bond dissociation enthalpies (BDEs) using the radical equilibration electron paramagnetic resonance technique. This revealed that the O-H BDEs in 5-pyrimidinols are, on average, about 2.5 kcal mol(-1) higher than those in equivalently substituted phenols. The results are in good agreement with theoretical predictions, and confirm that substituent effects on the O-H BDE of 5-pyrimidinol are essentially the same as those on the Obond;H BDE in phenol. The kinetics of the reactions of these compounds with peroxyl radicals has been studied by their inhibition of the AIBN-initiated autoxidation of styrene, and with alkyl and alkoxyl radicals by competition kinetics. Despite their larger O-H BDEs, 5-pyrimidinols appear to transfer their phenolic hydrogen-atom to peroxyl radicals as quickly as equivalently substituted phenols, while their reactivity toward alkyl radicals far exceeds that of the corresponding phenols. We suggest that this rate enhancement, which is large in the case of alkyl radical reactions, small in the case of peroxyl radical reactions, and nonexistent in the case of alkoxyl radical reactions, is due to polar effects in the transition states of these atom-transfer reactions. This hypothesis is supported by additional experimental and theoretical results. Despite this higher reactivity of 5-pyrimidinols towards radicals compared to phenols, electrochemical measurements indicate that they are more stable to one-electron oxidation than equivalently substituted phenols. For example, the 5-pyrimidinol analogues of 2,4,6-trimethylphenol and butylated hydroxytoluene (BHT) were found to have oxidation potentials approximately 400 mV higher than their phenolic counterparts, but reacted roughly one order of magnitude faster with alkyl radicals and at about the same rate with peroxyl radicals. The 5-pyrimidinol structure should, therefore, serve as a useful template for the rational design of novel air-stable radical scavengers and chain-breaking antioxidants that are more effective than phenols.     

The Fundamental Basis for Cyclopolymerization. VII. A Cyclopolymerization Study of Certain Allylcycloalkenes

The cyclopolymerization characteristics of 3-allylcyclopentene, 3 allylcyclopentene, 3-allylcyclohexene, and 4-allylohexene were studied and the extent of their cyclopolymerization by cationic initiation were compared with previously reported solvolysis results involving the same intermediate carbonium ion. The results of this study were also compared with previously reported results on 4-vinylcyclohexene and 1, 4-dimethylenecyclohexane. The allylcycloalkenes were also polymerized by metal alkyl coordination catalysts and the extent of cyclization in each case was determined. The polymers derived from these monomers invariably contained polymeric fractions (27 to 99%) which were soluble in non-polar organic solvents. Calculations based on NMR spectral data indicated the cationic polymers were 68 to 95% cyclized. The extent of cyclization was found to parallel the interolefinic separation in the monomer. Coordination polymerization yielded somewhat lower ratios of cyclizations (54 to 80%) in all cases except for 4-allylcyclohexene. 4-Allylcyclohexene gave only 5 to 54% cyclization, 4-Vinylcyclohexene, 3-allylcyclopentene, and 3-allylcyclohexene produced soluble copolymers with maleic anhydride. Elemental analysis indicated the composition of these copolymers to be 2:1 molar in maleic anhydride and diene units. A cyclic copolymerization mechanism suggested the formation of a multicyclic repeating unit. The other monomers gave crosslinked polymers since maleic anhydride could not be incorporated into a six-membered ring.     

Gas chromatographic determination of phenol compounds with automatic extraction and derivatization

Two gas chromatographic procedures for the determination of a variety of substituted phenols in water samples are described. The phenols were extracted or extracted-derivatized by using a continuous liquid-liquid extraction-derivatization system and quantified with flame ionization detection. Ethyl acetate was found to be the most efficient solvent for phenols whereas n-hexane yielded essentially the same recoveries for derivatized phenols. Between 0.1 and 300 mg/l of the different phenols can be detected with a relative standard deviation 1.1 and 3.7%. The acetate esters of six phenols were formed by the direct addition of acetic anhydride to the organic extractant. The stable acetate esters thus formed were isolated by using a standard dimethyl polysiloxane gas chromatographic column.     

Simulating phenol high-performance liquid chromatography retention times as the pH changes. Mobile phase pH versus buffer pH

The HPLC retention times of several substituted phenols have been measured and simulated using Advanced Chemistry Development's LC simulator, using 50% acetonitrile (ACN) as the mobile phase. For alkyl- and nitro-substituted phenols, the quality of the simulation improves when pH of the mobile phase is estimated and used in the simulation. Simply using the pH of the buffer gives simulation results that are not as close to the actual retention times. However, the opposite is the case for halogenated phenols. The pK(a) values in 50% ACN for some of these phenols have also been determined, which tend to be one unit higher than the aqueous pK(a) values reported in the literature.     

Mannich反应合成3,6(8)-二取代-2,4-二氢-1,3-苯并噁嗪及其杀菌活性

以取代苯酚、多聚甲醛和取代苯胺为原料,在无催化剂的条件下,通过Mannich缩合反应合成了一系列新型3,6(8)-二取代-2,4-二氢-1,3-苯并噁嗪类化合物。 结果表明,取代苯酚和取代苯胺的取代基为供电子基时,合成产物的产率高于吸电子取代基的。 产物的结构用1H NMR、13C NMR、IR和MS等进行了表征。 初步测试了目标化合物的杀菌活性,部分化合物具有较好的杀菌活性。 当浓度为25 mg/L时,化合物4j和4d对菌核病菌的抑制率分别为86.1％和81.5％,化合物4i对灰霉病菌的抑制率为81.6％。     

Die säurekatalysierte Isomerisierung von 7-Oxabicyclo[2.2.1]-heptadien- und Oxepin-Derivaten [1]

The acid catalyzed isomerization of several substituted oxanorbornadienes 4 and oxepines 10 - easily available from 4 by a photochemical and a consecutive thermal step - allows the synthesis of several highly substituted phenols and 2,4-cyclohexadienones in a straightforward manner and with good to excellent yields. The formation of the methoxycarbonyl-hexadienes 18e and 18f upon photolysis of 9e and 17f in methanol supports the structure elucidation. The relative importance of the McLAFFERTY and EMERY effects in the mass spectral degradation of methoxycarbonyl and methyl substituted phenols are discussed.     

胶束催化体系中的对映选择性环醚化反应

The enantioselective cycloetherification of substituted keto phenols into their corresponding dihydrobenzofuran derivatives was carried out using hydrogen peroxide and chiral quaternary ammonium iodide in micellar media. This approach increased the conversion rate of cycloetherification and also widened the scope of this particular reaction for various substituted keto phenols with electron withdrawing as well as electron donating functionalities. The use of a surfactant in the cycloetherification reaction ...     

Oxidative nucleophilic substitution of hydrogen in nitroarenes with trifluoromethyl carbanions. Synthesis of trifluoromethyl phenols

Trifluoromethyl carbanions generated from the Ruppert reagent and TASF add to highly electron-deficient nitroarenes to produce σ^H adducts subsequently oxidized with dimethyldioxirane to substituted trifluoromethyl phenols.     

Microdetermination of phenols, carboxylic acids and phenolic acids by potentiometric and visual titrations in dimethylformamide

Potentiometric titration of phenols with sodium methoxide in dimethylformamide, with a glass-calomel electrode system, is limited to monohydric phenols substituted with electron-attracting groups and dihydric phenols in which the two -OH groups are substituted in isolated benzene rings. Brilliant Orange has proved to be a suitable indicator in the titration of all types of mono- and dihydric phenols. Titan Yellow is recommended as indicator for the titration of carboxylic acids. Simultaneous visual titration of -OH and -COOH groups is also described. A detailed study with 62 structurally different compounds covering the various groups is reported, and a suitable procedure for the microdetermination of each class of these compounds with an error of +/- 0.2% absolute or less is presented.     

Separation of Phenols by Capillary Electrophoresis in a Polyethyleneimine-Coated Capillary

The use of polyethyleneimine-coated capillaries for the capillary electrophoretic separation of substituted phenols has been demonstrated. Efficient separation of phenols has been achieved in the coated capillaries.     

Silicalite as a stationary phase for HPLC

A molecular sieve known as Silicalite was used as the column packing for HPLC. Silicalite contains channels (or cavities) approximately 6 Å in diameter but, unlike most other molecular sieves, Silicalite is hydrophobic. The retention times of methyl ketones and substituted phenols containing n-alkyl groups increase with increasing chain length of the substituent. However, phenols with very bulky substituents appear to be excluded from the Silicalite channels and elute very quickly. Excellent separations were obtained for a number of compounds with only slight differences in chemical structure. These include phenol isomers with a primary- or secondary alkyl group, position isomers of substituted phenols, and aliphatic cis-trans isomers.     

Reactivity of phthalimide N-oxyl radical (PINO) toward the phenolic O-H bond. A kinetic study

The reactivity of the phthalimide N-oxyl radical (PINO) toward the OH bond of a series of substituted phenols was kinetically investigated in CH(3)CN. The reaction selectivity and the deuterium kinetic isotope effect were determined. Information on the kinetic solvent effect was also obtained with phenol as the substrate.