A decisive electronic effect of a bridgehead methoxy substituent on the electrophilic cage opening of 1,3-bishomocubanones

4-Methoxypentacyclo[5.3.0.0^2,5.0^3,9.0^,4,8] decan-6-ones 4 and 9 undergo an acid catalysed cage fragmentation to give tricyclodecenediones 6 and 10, respectively. With silver cations under basic conditions, an unusual oxidative cage fission reaction is observed leading to tetracyclo[4.3.0.0^2,40^3,8]nonan-5-one 7-carboxylic acids.     

Use of a methoxy substituent in controlling the stereochemistry of intramolecular iron-mediated diene/olefin cyclocoupling

A methodology for stereocontrol during the intramolecular coupling between cyclohexadiene--Fe(CO)(3) complexes and pendant alkenes is presented. Introduction of a methoxy group at the C(3) position of the diene moiety controls pre- and postcyclization rearrangements of the diene Fe(CO)(3) unit, allowing the preparation of spirolactams with defined relative stereochemistry and with a cyclohexenone framework, thus making this reaction a potentially valuable tool for the construction of quaternary carbon centers.     

Assessment of the methoxy substituent effect in the gas phase elimination of methoxyalkyl acetates

The gas phase elimination of 4-methoxybutyl acetate in the temperature range of 370–420°C and pressure range of 67–216 Torr is homogeneous, unimolecular and follows a first order kinetics. The rates have been measured in a static system and the reactions carried out in seasoned vessels. Steric acceleration seems to be an important factor when the methoxyalkyl chain of the ester is increased.

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4- 370–420°C 67–216 , . . .

     

ESR study of some methyl methoxy benzoates. Additivity model of substituent effects

The radical anions of several methyl methoxy benzoates are obtained by an in situ electrochemical method. ESR spectra of these radicals and u.v. spectra of their parent compounds are analyzed in order to study the change of conformation in the ortho substituted esters, when these are reduced. The effects of the substituents on the hyperfine coupling constants (HCCs) are analyzed by means of an additivity model.     

Polymeric siloxanes with a substituent and the spirobenzopyran moiety: Effect of polar substituent on the photochromic properties

Oligomeric polysiloxanes having the spirobenzopyran moiety and various substituents were prepared. The polymers were photochromic; the color changed from colorless to red on UV irradiation and the color faded on visible irradiation or on standing in the dark. The thermal decoloration was depressed by the polar substituents. However, the effect of the bulky substituent, which had been observed in the rigid siloxane resins, was not detected. In the inorganic/organic hybrid siloxane gels, the silica/(spirobenzopyran-bonding polysiloxane) system and the (spirobenzopyran-bonding silica)/polysiloxane system, the thermal decoloration was also affected by the polar substituent introduced into the polysiloxane portion. The effect was larger in the first case than in the second. The result can be interpreted by the term of the preferential diffusion of polar spirobenzopyran to the vicinity of the polar substituents during the gelation.     

Modulating light‐tunable acid sensitivity of a bioinspired polymer simply by adjusting the position of a single methoxy substituent

This article describes a rhodopsin‐inspired photosensitive polymer whose light‐tunable acid sensitivity can be widely modulated simply by adjusting the position of a single methoxy substituent in the aromatic rings of cinnamyl groups. The well‐defined poly(5‐ethyl‐5‐methacryloyloxymethyl‐2‐(p‐methoxystyryl)‐[1,3]dioxane) (PEMpMSD) and poly(5‐ethyl‐5‐methacryloyloxymethyl‐2‐(o‐methoxystyryl)‐[1,3]dioxane) (PEMoMSD) as well as poly(5‐ethyl‐5‐methacryloyloxymethyl‐2‐styryl‐[1,3]dioxane) were synthesized via reversible addition‐fragmentation chain transfer (RAFT) process. The results demonstrated that the para‐methoxy substitution of EMpMSD monomer led to the more shortened initialization period and rapid chain propagation of RAFT process than 5‐ethyl‐5‐methacryloyloxymethyl‐2‐styryl‐[1,3]dioxane monomer under mild visible light radiation at 25 °C. The ortho‐methoxy substitution of PEMoMSD led to high degree of photoinduced Z‐isomerization over 80%. Moreover, the para‐methoxy substitution of PEMpMSD led to the rapid hydrolysis of the cyclic acetal linkages in ambient acid media, while the ortho‐methoxy substitution of PEMoMSD slowed down this hydrolysis. This hydrolysis slowed down on Z‐isomerization particularly in PEMoMSD. These effects widely broadened the tunability of the light‐modulated acid sensitivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

New homochiralortho-palladated matrix bearing a bulky substituent at the carbon stereocenter

A new homochiral dimericortho-palladated complex bearing a bulkytert-butyl substituent at the carbon stereocenter was synthesized from optically activeN,N-dimethyl-α-tert-butylbenzylamine. Regioselective activation of only the aromatic C−H bond was shown to occur during the cyclometallation process proceeding under very mild conditions due to steric effects. Spectral characteristics of mononuclear derivatives of the new dimeric complex indicate that the five-membered palladacycle exists predominantly in one of two possible chiral conformations with the axial position of thetert-butyl substituent. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1375–1384, July, 1997.     

Effect of a proximal substituent on the triruthenium dodecacarbonyl-catalyzed reductive carbonylation of nitroarenes

Three nitroarenes were submitted to Ru₃(CO)₁₂-catalyzed reductive carbonylation in acetonitrile and in cis-cyclooctene. The main reaction products were the corresponding amines, ureas and six- or five-membered cyclization products. Optimization of the reaction varying the temperature, the CO pressure, the catalyst/substrate ratio and the reaction time and a statistical analysis of conversion and selectivity data allow to suggest a reaction mechanism in some reaction conditions.     

Effect of substituent structure on pyrimidine electrophilic substitution: a rebuttal

The report about a series of unexpected and obscure effects influencing the electrophilic nitrosation of activated pyrimidines (Tetrahedron 2007, 63, 5394) was shown to be erroneous. Instead of electrophilic substitution at position 5 of the pyrimidine ring, N-nitrosation of the secondary amino group in the 4-position of the pyrimidine ring took place. Moreover it was shown that the synthetic sequence for the preparation of purines is also incorrect.     

Incomparably easy migration of functionalized enol substituent in pyrrole ring

Functionalized pyrroleьvь? enols, 2-(1-hydroxy-2.2-dicyanoethenyl)-1-methylpyrroles, at heating (75–135°C) unexpectedly readily rearranged in high yield into 3-isomers. Evidently the migration of the enol fragment involves a mesomeric zwitterion formed as a result of an intra- and intermolecular autoprotonation of the pyrrole ring by the acidic enol hydroxy group. Under similar conditions no migration of the ethenyl moiety occurred in 2-(1-hydroxy-2-carbamoyl-2-cyanoethenyl)-1-methylpyrroles. The quantum-chemical calculations (MP2/6-311G**) show a clear-cut distinction in the relative stability of 2- and 3-isomers of 1H- and 1-methylhydroxyethenylpyrroles: in the former case the 2-isomer is more stable, whereas in the 1-methyl-substituted compound, the 3-isomer.     

Effect of the nature of a fluorinated substituent on the synthesis of functionalized 1,3-diketones

Russian Chemical Bulletin - The synthesis of alkali metal and copper(ii) 1-polyfluoroalkyl-4,4-dimethoxypentane-1,3-dionates is reported. The subsequent treatment of these compounds with oxalic...     

Effect of substituent structure on pyrimidine electrophilic substitution

In an investigation into the electrophilic nitrosation reactions of a series of 4,6-disubstituted pyrimidine derivatives, a subtle interplay between the electronic nature of the C-4 and C-6 substituents and reactivity was found where these were chloro-, mono- or disubstituted amino groups. Effects such as the presence of an aryl group or two alkyl groups on the amino moiety impede the progress of the reaction despite the presence of a second activating group.     

Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: gas phase reactions between amines and the methoxy methyl cation

The reactions of various amines (RNH(2); R = H, CH(3), C(2)H(5) and i-C(3)H(7)) with the methoxy methyl cation (CH(2)OCH(3)(+)) have been investigated using an FT-ICR mass spectrometer, and the experimental results are supplied with ab initio calculations. The amines show clear trends in their reactivities with variable degree of: 1) nucleophilic substitution, 2) addition-elimination and 3) hydride abstraction. In all cases addition-elimination dominates over nucleophilic substitution, and for R not equal H the observed reactions occur at the collisional limit. The potential energy profiles for all three reaction types correlate with the basicities of the amines; the more basic amine-the more favourable is the reaction; in other words: nucleophilicity follows basicity in the gas phase.     

Effect of substituent distribution on water solubility of O-methylcellulose

The effect of substituent distribution on the water solubility of O-methylcellulose (MC) was re-examined to elucidate the lower limit of the degree of substitution (DS) in water-soluble MC. To this end, a series of 2,3-MCs which are regioselectively substituted at the C-2 and C-3 hydroxyl groups were prepared by homogeneous methylation. It was found that the lower limit for the DS value of water-soluble 2,3-MC was almost the same as that for MCs having even distributions of substituents along the cellulose chain as well as in the anhydroglucose units. This revised version was published online in August 2006 with corrections to the Cover Date.     

13C NMR study on the methoxy carbon chemical shifts in chloro-substituted anisoles and guaiacols

The ¹³C NMR chemical shifts of methoxy carbons in chlorinated anisoles and guaiacols have been measured for acetone-d₆ solutions. Multiple linear regression analysis, and also ‘simple sum rule’ calculations, have been used to estimate the effects of the chlorine atoms (the position and degree of substitution) on the chemical shifts. The most important effects have shown to be due to the chlorine atoms adjacent to the methoxy and hydroxy substituents. For chlorinated guaiacols, the greatest effect is due to the chlorine atom adjacent to the methoxy group. For chlorinated anisoles, the substituents adjacent to the methoxy group (2,6-disubstitution) cause large effects. For both groups of compounds, the chemical shifts are also greatly influenced by the number of chlorine substituents. Using the three most important independent variables, the average differences between the observed and calculated chemical shifts are ca 0.2 ppm for anisoles and 0.1 ppm for guaiacols. For chloroguaiacols, the corresponding difference was only 0.1 ppm when calculations were performed using single substituent effects.     

Correlations of chemical shifts of saturated carbon atoms that have a directly bonded substituent

The dependence of the chemical shifts, δ, of saturated carbon atoms upon the nature of the directly bonded substituent is attributed to three factors (1) electronegativity E, (2) field effect, W, and (3) heavy atom ettect, Q. Ten series of compounds (five aliphatic and five cyclic) have been correlated with the equation δ = aE + W + Q+ c where a and c are constants.     

Effect of a lateral substituent on the mesomorphic properties of ferroelectric side chain liquid crystalline polysiloxanes

The synthesis of side chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and ( S )-2-methylbutyl 4-\[(4-oxybiphenyl-4-yl)carbonyloxy]-3-fluorobenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for all synthesized monomers and polymers. All three precursor olefinic monomers reveal cholesteric and smectic A phases. The olefinic monomer which contains two oligooxyethylene units in the spacer is the only one which reveals a twist grain boundary A phase and a blue phase, besides the cholesteric and smectic A phases. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The mesomorphic behaviours of the monomers and polymers are compared with those of the corresponding monomers and polymers without the lateral fluoro substituent. The results seem to demonstrate that incorporating a lateral fluoro substituent in the mesogenic cores of the monomers affects not only the mesophase thermal stability, but also the nature of the mesophases formed. However, incorporating a lateral fluoro substituent in the mesogenic cores of the polymers affects only the thermal stability of the mesophases formed. The lateral fluoro substituent has a more profound effect on the mesomorphic behaviour for the monomers than that for the polymers.     

Mechanism of the migration of the substituent in 1,2,3,7a-tetrahydroimidazo[1,2-b]isoxazole derivatives

Russian Chemical Bulletin - The thermolysis of 1,2,3,7a-tetrahydroimidazo[1,2-b]isoxazole derivatives results in intramolecular rearrangements by two main pathways. One rearrangement affords...