Tert-alkyl Groups Research Articles

Study of Direct N7 Regioselective tert-Alkylation of 6-Substituted Purines and Their Modification at Position C6 through O, S, N, and C Substituents.

A new N7 direct regioselective method allowing the introduction of tert-alkyl groups into appropriate 6-substituted purine derivatives is developed. This method is based on a reaction of N-trimethylsilylated purines with a tert-alkyl halide using SnCl4 as a catalyst. In this work, we study the structure and optimal reaction conditions leading to the N7 isomer and in some cases also to the N9 isomer. The main goal is devoted to preparing 7-(tert-butyl)-6-chloropurine as a suitable compound for other purine transformations. The stability of the tert-butyl group at the N7 position is tested for classic model reactions, leading to the preparation of new 6,7-disubstituted purine derivatives, which is also interesting from the point of view of possible biological activity.

Transition-Metal-Free Approach for Z-Vinyl Fluorides by Hydrofluorination of Alkynes bearing SF4 and SF5 Groups.

The synthesis of vinyl fluorides plays a crucial role in various scientific disciplines, including pharmaceutical and materials sciences. Herein, we present a direct and stereoselective hydrofluorination method for the synthesis of Z isomers of vinyl fluorides from alkynes containing unexplored SF5 and SF4 groups. Our strategy employed tetrabutylammonium fluoride (TBAF) as a fluorine source. It demonstrates high compatibility with aryls, biaryls, heteroaryls, and tert-alkyl groups, allowing facile incorporation of SF5 and SF4 groups across the triple bond without any transition-metal catalysts. This approach avoids the potential decomposition of the SF5 or SF4 units via coordination with transition metals or acidic protic sources. Remarkably, this transformation proceeded at room temperature without any additional additives, providing the Z isomer of vinyl fluorides in excellent yield and high selectivity. The presence of a water molecule as a hydrate in TBAF is essential for efficient conversion. This methodology opens new avenues for the synthesis of enchanting SF5 - and SF4 -containing fluorinated vinylic scaffolds, thereby providing advanced opportunities for novel drug discovery and fluorinated polymers.

Unprecedented 1,3-tert-butyl migration via the C-N single bond scission of isonitrile: an expedient metal-free route to N-sulfonyl amidines.

An unprecedented 1,3-migration of the tert-butyl group was observed while reacting tert-butyl isonitrile with N,N-dibromoaryl sulfonamides and nitrile. The reaction involves the simultaneous C-N single bond scission of isonitrile and the migration of the tert-alkyl group to the adjacent unsaturated nitrogen centre of the nitrile precursor, which eventually results in the formation of N-sulfonyl amidine. This method constitutes a new route for sulfonyl amidine, which does not rely on transition metals. The protocol exhibits a significant advantage in terms of substrate scope and additionally offers an easy synthesis route to guanidine molecules.

Factors Affecting Migration of Tertiary Alkyl Groups in Reactions of Alkylboronic Esters with Bromomethyllithium

The reactions of bromomethyllithium with tert-alkylboronic esters could be of great potential for the formation of quaternary carbon centers but often give poor yields/conversions. Calculations and experimental evidence show that tert-alkyl groups migrate less effectively than other types of alkyl group in such reactions and that O-migration competes. Furthermore, slow/incomplete capture of the bromomethyl reagent by the boronic ester is a problem in more hindered systems, and an additional competing reaction, possibly Li-Br exchange on the bromomethylborate species, also leads to lower yields of migrated products. Based on this, experimental protocols have been devised in which the competing reactions are largely suppressed, leading to higher conversions to migrated product for several substrates.

A New Class of Organosuperbases, N‐Alkyl‐ and N‐Aryl‐1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐ylidene Amines: Synthesis, Structure, pKBH+ Measurements, and Properties

A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized from N,N'-dialkylthioureas and 3-hydroxy-2-butanone and their basicities were measured in acetonitrile. The derivatives with tert-alkyl groups on the imino nitrogen were found to be more basic than the tBuP(1) (pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by (13)C NMR chemical shifts or by the calculated ΔNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino-substituents, including electron-acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas-phase basicity becomes more dependent on the field-inductive effect, polarizability, and resonance effects of the substituent.

Rate and equilibrium effects of tert-alkyl groups on rotamerization in 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyl(di-tert-alkyl)methanols: an IR, NMR, kinetics and MM studyElectronic supplementary information (ESI) available: additional experimental data. See http://www.rsc.org/suppdata/p2/b2/b203714a/

Di-1-adamantyl and (1-adamantyl)(tert-butyl) analogues are compared with the previously studied 3- or 3- and 4-substituted 2-thienyl(di-tert-butyl)methanols. The equilibrium constants for syn–anti rotamerization ([syn]/[anti]) are slightly greater than for the smaller di-tert-butyl derivatives. In the intramolecularly hydrogen-bonded anti rotamers, neither the 1H NMR shift of the hydroxy proton nor the OH stretching frequency, both indicators of intramolecular hydrogen bond strength, is greatly affected by a change in the tert-alkyl group; these changes in the equilibrium constants must, therefore, be attributed to variations in steric effects. The rotation barriers for the compounds with the larger tert-alkyl groups are much enhanced and better differentiated. In all three sets the syn→anti and anti→syn rotation barriers are linearly correlated, and either can be correlated with the free energy difference. Nevertheless, the data do not meet the criteria for a classical Leffler–Grunwald-type rate-equilibrium relationship. Molecular mechanics calculations (MMFF94 force field) account fairly well for the variation in the free energy difference for rotamer pairs of the di-1-adamantyl, (1-adamantyl)(tert-butyl) and di-tert-butyl derivatives, but slightly overestimate the small differences in the equilibrium constants for the three series. The calculated rotation barriers for the di-tert-butyl compounds are about 7 kcal mol−1 higher than those observed. Those for 2-anisyl-, phenyl- and 2-tolyldialkylmethanols are increasingly overestimated as the rotation barrier rises, but a good correlation ranging over 20 kcal mol−1 is obtained; this correlation is not coincident with that for the thiophene derivatives.

Isolation of an oxomanganese(V) porphyrin intermediate in the reaction of a manganese(III) porphyrin complex and H2O2 in aqueous solution.

The reaction of [Mn(TF(4)TMAP)](CF(3)SO(3))(5) (TF(4)TMAP=meso-tetrakis(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-aniliniumyl)porphinato dianion) with H(2)O(2) (2 equiv) at pH 10.5 and 0 degrees C yielded an oxomanganese(V) porphyrin complex 1 in aqueous solution, whereas an oxomanganese(IV) porphyrin complex 2 was generated in the reactions of tert-alkyl hydroperoxides such as tert-butyl hydroperoxide and 2-methyl-1-phenyl-2-propyl hydroperoxide. Complex 1 was capable of epoxidizing olefins and exchanging its oxygen with H(2) (18)O, whereas 2 did not epoxidize olefins. From the reactions of [Mn(TF(4)TMAP)](5+) with various oxidants in the pH range 3-11, the O-O bond cleavage of hydroperoxides was found to be sensitive to the hydroperoxide substituent and the pH of the reaction solution. Whereas the O-O bond of hydroperoxides containing an electron-donating tert-alkyl group is cleaved homolytically, an electron-withdrawing substituent such as an acyl group in m-chloroperoxybenzoic acid (m-CPBA) facilitates O-O bond heterolysis. The mechanism of the O-O bond cleavage of H(2)O(2) depends on the pH of the reaction solution: O-O bond homolysis prevails at low pH and O-O bond heterolysis becomes a predominant pathway at high pH. The effect of pH on (18)O incorporation from H(2) (18)O into oxygenated products was examined over a wide pH range, by carrying out the epoxidation of carbamazepine (CBZ) with [Mn(TF(4)TMAP)](5+) and KHSO(5) in buffered H(2) (18)O solutions. A high proportion of (18)O was incorporated into the CBZ-10,11-oxide product at all pH values but this proportion was not affected significantly by the pH of the reaction solution.

Colloidal systems containing free radical-forming particles and composites on their basis

Controlled surface activity and reactivity of new carbon-chain functional surface-active oligoperoxides (FSAP) and derived metal complexes (OMC) with side and end di-tertiary and tert-alkyl (aryl) peroxidic, respectively, and other active functional groups cause the possibility of their tailored utilization as emulsifiers, surface-active initiators and modifiers of the phase boundaries of liquid, solid and mixed phases in different colloidal systems in a wide temperature range. New materials can be developed such as water and hydrocarbon polymer dispersions, artificial water dispersions of unsaturated polyesters and alkyd resins, polymer/polymeric blends, active glass and carbon fibers, dispersed fillers, reinforced and filled polymer composites with the definite special properties. Methods for the obtaining and the application of these materials are described.

Competing inter- and intramolecular hydrogen bonding: solvent-driven rotamerization in 3,4-(ethylenedioxy)-2-thienyldi(tert-alkyl)methanols

3,4-(Ethylenedioxy)-2-thienyldi(tert-alkyl)methanols exist in two rotameric forms, the equilibrium constant for the anti⇌syn rotamerization depending on the solvent. The equilibrium constant ([syn]/[anti]) is close to unity in benzene and chloroform, regardless of the tert-alkyl groups (tert-butyl or 1-adamantyl). This rises to about 10 in pyridine and 20 in DMSO (both at 25 °C), where intermolecular hydrogen bonding clearly prevails over intramolecular. For the di(tert-butyl) derivative there is a good correlation between the equilibrium constant (log K) and the hydrogen bond basicity parameter (βH2). The temperature dependence of the rotamer ratio in strongly hydrogen-bonding solvents indicates that the enthalpy term favours the syn isomer and the entropy term the anti. Rotation barriers have been measured in both hydrogen-bonding and non-hydrogen-bonding solvents. The differences in the equilibrium constants reflect the solvent effect upon the anti→syn isomerization, which is shown to be “solvent-driven” in the case of the di(1-adamantyl) derivative in pyridine.

New Insights into the Mechanisms of O−O Bond Cleavage of Hydrogen Peroxide andtert-Alkyl Hydroperoxides by Iron(III) Porphyrin Complexes

The mechanisms of heterolytic versus homolytic O−O bond cleavage of H2O2, tert-butyl hydroperoxide (t-BuOOH), 2-methyl-1-phenyl-2-propyl hydroperoxide (MPPH), and m-chloroperoxybenzoic acid (m-CPBA) by iron(III) porphyrin complexes have been studied by carrying out catalytic epoxidations of cyclohexene in protic solvent. In these reactions, various iron(III) porphyrin complexes containing electron-withdrawing and -donating substituents on phenyl groups at the meso position of the porphyrin ring were employed to study the electronic effect of porphyrin ligands on the heterolytic versus homolytic O−O bond cleavage of the hydroperoxides. In addition, various imidazoles were introduced as axial ligands to investigate the electronic effect of axial ligands on the pathways of hydroperoxide O−O bond cleavage. Unlike the previous suggestions by Traylor, Bruice, and co-workers, the hydroperoxide O−O bonds were found to be cleaved both heterolytically and homolytically and partitioning between heterolysis and homolysis was significantly affected by the electronic nature of the iron porphyrin complexes (i.e., electronic properties of porphyrin and axial ligands). Electron-deficient iron porphyrin complexes show a tendency to cleave the hydroperoxide O−O bonds heterolytically, whereas electron-rich iron porphyrin complexes cleave the hydroperoxide O−O bonds homolytically. The heterolytic versus homolytic O−O bond cleavage of the hydroperoxides was also found to be significantly affected by the substituent of the hydroperoxides, ROOH (R = C(O)R‘, H, C(CH3)3, and C(CH3)2CH2Ph for m-CPBA, H2O2, t-BuOOH, and MPPH, respectively), in which the tendency of O−O bond heterolysis was in the order of m-CPBA > H2O2 > t-BuOOH > MPPH. This result indicates that the O−O bond of hydroperoxides containing electron-donating tert-alkyl groups such as t-BuOOH and MPPH tends to be cleaved homolytically, whereas electron-withdrawing substituents such as an acyl group in m-CPBA facilitates O−O bond heterolysis. Since we have observed that the homolytic O−O bond cleavage of hydroperoxides prevails in the reactions performed with electron-rich iron porphyrin complexes and with hydroperoxides containing electron-donating substituents such as the tert-alkyl group, we suggest that the homolytic O−O bond cleavage is facilitated when more electron density resides on the O−O bond of (Porp)Fe(III)-OOR intermediates. We also present convincing evidence that the previous assertion that the reactions of iron(III) porphyrin complexes with hydrogen peroxide and tert-alkyl hydroperoxides invariably proceed by heterolytic O−O bond cleavage in protic solvent and that the failure to obtain high epoxide yields in iron porphyrin complex-catalyzed epoxidation of olefins by hydroperoxides is due to the mechanism of heterolytic O−O bond cleavage followed by a fast hydroperoxide oxidation is highly unlike.

Molecular addition compounds. 16. New, highly reactive borane adducts with N,N-dialkyl-tert-alkylamines for hydroboration

Several N,N-diethyl-tert-alkylamines, such as N,N-diethyl-2-methyl-2-butylamine (1, t-PentNEt2), N,N-diethyl-2,3-dimethyl-2-butylamine (2, t-HexNEt2), N,N-diethyl-2,3,3-trimethyl-2-butylamine (3, t-HeptNEt2), and N,N-diethyl-1,1,3,3-tetramethylbutylamine (4, t-OctNEt2) with varying steric bulk around nitrogen (by changing the tert-alkyl group) have been prepared and examined as borane carriers. The complexing ability of these N,N-diethyl-tert-alkylamines with borane decreases in the order: t-BuNEt2 > t-PentNEt2 > t-HeptNEt2 > t-HexNEt2 > or = t-OctNEt2. From these preliminary studies, the more promising tert-octyldialkylamines were selected for detailed studies. The optimum steric bulk around the nitrogen atom was established by comparing various tert-octyldialkylamines containing variable steric requirements for both the alkyl groups. The complexing ability of these amines with borane decreases in the order shown: t-OctNMe2 (5) > t-OctNEtMe (6) > t-OctN-(CH2CH2)2O (7) > t-OctNEt2 (4) > t-OctNBuiMe (8) > t-OctNPr(n)2 (9). The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. Among the various tert-octyldialkylamine-boranes prepared and examined, only t-OctNEt2 (4) forms a highly reactive liquid borane adduct, which hydroborates 1-octene in tetrahydrofuran rapidly at room temperature. Accordingly, detailed hydroboration studies with this new, highly reactive amine-borane adduct, t-OctEt2N:BH3 (10) and representative mono-, di-, tri-, and tetra-substituted olefins were carried out at room temperature (22 +/- 3 degrees C) in selected solvents, tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane and dichloromethane. Simple unhindered olefins were hydroborated to the trialkylborane stage, whereas hindered olefins were partially hydroborated to the mono or dialkylborane stage. The hydroborations can be carried out conveniently in a variety of solvents. The amine-borane adduct showed enhanced reactivity in dioxane but low reactivity in dichloromethane. The alkylboranes obtained after hydroboration were oxidized with hydrogen peroxide/sodium hydroxide and the product alcohols were obtained in quantitative yields, as established by GC analysis. The carrier amine was recovered by simple acid-base manipulations in good yield and can be readily recycled back to the borane adduct.

Thermochemistry of phenols: buttress effects in sterically hindered phenols

The standard (po= 0.1 MPa) molar enthalpies of formation ΔfHmo(l, or cr) at the temperature 298.15 K were measured by means of combustion calorimetry for 2,3,6-tri-methylphenol, 2,4,6-tri-methylphenol, 2,6-di-iso-propylphenol, 2-tert-butyl-6-methylphenol, 2-tert-butyl-4,6-di-methylphenol, 2,6-di-tert-butylphenol, 2,6-di-tert-buty-4-methylphenol, and 2,4,6-tri-tert-butylphenol. The standard molar enthalpies of sublimation (or vaporization) of these compounds were obtained from the temperature dependence of the vapor pressure measured in a flow system. Molar enthalpies of fusionΔcrlHmo of the solid compounds were measured by d.s.c. Resulting values ofΔfHmo (g) were obtained at the temperature 298.15 K and used to derive strain enthalpies of alkylphenols. The intramolecular interactions were discussed in terms of the enthalpic contribution of the substituents. The buttress interaction of tert-alkyl groups with hydroxyl t-Bu-OH-t-Bu was found to be 5.0 kJ · mol−1. Other buttress effects of methyl, iso-propyl-, and tert-alkyl substituents with the OH-group were found to be negligible within ±(1 to 2)kJ · mol−1. These values provided a further improvement on the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.

Geminal Dialkylation and Alkylative Reduction of Aliphatic Aldehydes

gem-Dialkylation or alkylative reduction of α-unbranched aliphatic aldehydes is easily carried out by replacing the carbonyl oxygen with the gem-dihalide functionality followed by substitution of each halogen (bromine or iodine) by two n-alkyl groups or one sec- or tert-alkyl group and one hydrogen atom using higher-order dialkyllithium cyanocuprates.

Cation-exchange resin (Amberlyst-15) catalyzed alkylation of phenol with unhydrogenated PAO decene trimer. Rearrangement of tert-alkylphenols to sec-alkylphenols

Alkylation of phenol with decene trimer, representative of poly-α-olefin (PAO) oligomers in general, catalyzed by Amberlyst-15, affords mostly o- and p-tert-alkylphenols at temperatures below 75°C, but o- and p-sec-alkylphenols above 100°C, where tert-alkyl groups show great propensity to rearrange to the more stable sec-alkyl groups

EPR studies on electron transfer reactions between O-benzoyl-N-alkylhydroxylamines and perfluoroacyl peroxides. Generation of n- and sec-alkyl perfluoroacyl nitroxides and sec- and tert-alkyl perfluoroalkyl nitroxides

Both EPR studies and product analysis have disclosed that the oxidation of O-benzoyl-N-alkylhydroxylamines (1, 4, 7) by perfluoroacyl peroxides (2) is an electron transfer-initiated process. Depending on the nature of the alkyl groups in the substrates, the caged radical pair CP1 (RN OCOPh, RfCOO) may react through different radical pathways resulting in different nitroxides along with the neutral products. With primary, benzyl and secondary alkyl groups, a 1,2-acyl shift becomes the predominant pathway resulting in acyl nitroxides (3, 5). With tert-alkyl groups such as tert-butyl, tert-alkyl perfluoroalkyl nitroxides (8) are formed via β-scission of both RN*OCOPh and RfCOO*. A general mechanistic pathway is proposed for the titled reactions generating the quite useful fluorinated nitroxides.

Synthesis and Characterization of Thermally Stable Polymers through Anionic Polymerization of tert-Alkyl Crotonates

Some alkyl crotonates bearing tert-alkyl groups, i.e., tert-butyl, tert-amyl, 1-adamantyl and 3,5-dimethyl-1-adamantyl crotonates were prepared and polymerized with sec-butyllithium as an anionic catalyst in toluene or THF. The resulting polymers were confirmed to consist of poly(substituted methylene) structure by IR and NMR spectroscopies. The polymers bearing adamantyl groups had more resistance to hydrolysis, whereas the tert-butyl and amyl esters were readily hydrolyzed. The introduction of the adamantyl groups also increased glass transition temperature and decomposition temperature of the polymer. It was revealed that the polymers bearing the tert-butyl and amyl esters decomposed via a two-step mechanism, resulting in the formation of poly(crotonic acid) accompanied with elimination of corresponding olefins from the ester groups, but the polymers containing adamantyl groups showed excellent thermal stability.

Some novel structural and chemical aspects of Cp-substituted bent metallocene complexes

Abstract

ChemInform Abstract: Polyfluoro‐tert‐alkylsulfenyl Chlorides.

AbstractTreatment of the disulfides (I) with chlorine gives the sulfenyl chlorides (II).

Polyfluoro-tert-alkylsulfenyl chlorides

Polyfluoroalkylsulfenyl chlorides with tert-alkyl groups were obtained and these compounds were found to be similar to sulfenyl chlorides with primary polyfluoroalkyl groups in electrophilic addition at the C=C bond and are distinguished only in somewhat reduced reactivity.

N-dealkylation of 2-(tert-butyl)-3-hydroxy-3-(4-chlorophenyl)isoindolinone and n-(tert-alkyl)-2-aroylbenzamides in concentrated sulfuric acid

It has been established that 2-(tert-butyl)-3-hydroxy-3-(4-chlorophenyl)isoindolinone and N-(tert-Alkyl)-2-aroylbenzamides are dealkylated in concentrated sulfuric acid to give 3-hydroxy-3-arylisoindolinones. The reaction is realizable. only when there is a tert-alkyl group attached to the nitrogen atom. The reaction mechanism is discussed on the basis of data on the change with time in the electronic spectra of the investigated compounds in concentrated sulfuric acid and a comparison with the spectra of model structures.