Reactions of 3,5-di(tert-butyl)-1,2-benzoquinone with terminal acetylenes in the presence of phosphorus trichloride. ipso-Substitution of the tert-butyl group

The reactions of 3,5-di(tert-butyl)-1,2-benzoquinone with aryl-and alkylacetylenes in the presence of phosphorus trichloride afford 4-aryl(alkyl)-8-tert-butyl-2,6-dichloro-2-oxo-2H-benzo[e][1,2]oxaphosphinines as the major ipso-substitution products of the tert-butyl group by the chlorine atom. 4-Aryl(alkyl)-6,8-di(tert-butyl)-2,5-dichloro-2-oxo-and 4-aryl(alkyl)-6-tert-butyl-2,8-dichloro-2-oxo-2H-benzo[e][1,2]oxaphosphinines were obtained as the minor products. The structures of the stable representatives of this series were confirmed by X-ray diffraction. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1845, September, 2007.     

Modification of pyridine-3-carboxamide (nicotinamide) by radical substitution

Pyridine-3-carboxamide ( 1 ) was reacted with alkyl radicals to give mono-, di-, and tri-alkylated products. The t-butyl radical gives only 6-t-butylpyridine-3-carboxamide ( 4a ). The reactivity decreases in the order of t-butyl, isopropyl, and ethyl radicals. The product 4a reacts further with the 2-phthalimidoethyl radical to give 2- and 4-substituted products 9 and 10 , which were transformed into tetrahydronaphthyridinone derivatives 11 and 12 .     

Kinetics of heat-induced and photochemical transformations of quinonimines and their derivatives

Heat-induced transformations of N-[2,6-diisopropylphenyl]-3,5-di(tert-butyl)-, N-[2,6-diethylphenyl]-3,5-di(tert-butyl)-, and N-[2-methyl-6-ethylphenyl]-3,5-di(tert-butyl)-o-benzoquinonimines in nonane follow the first-order rate equation, whereas that of N-[2,5-di(tert-butyl)phenyl]-3,5-di(tert-butyl-o-benzoquinonimine obey the second-order rate equation. Kinetic parameters of these reactions have been determined. 4aH-Phenoxazine derivatives of quinonimines are intermediates of the heat-induced transformations following the first-order kinetics; under the irradiation with 405 nm light they undergo the ring opening to give the starting compounds with quantum yield close to unity.     

Phosphorus-containing derivatives of 2,6-di(tert-butyl)phenol: The antioxidant activity and properties of the corresponding phenoxyl radicals

The properties of phenoxyl radicals generated by the oxidation of mono-, di-, and triphosphorus derivatives of 2,6-di(tert-butyl)-4-methylphenol (ionol) were studied by ESR. These compounds exist as conformers that are interconvertible with a temperature-dependent rate. Numerical processing of the ESR spectra gave the thermodynamic and activation parameters that characterize the interconversion of the conformers. The antioxidant activities of the compounds were studied in a model oxidation of oleic acid and with biological objects. These phenols efficiently inhibited radical oxidation reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 744–750, April, 2007.     

6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2- benzoquinone]: Synthesis and properties

Preparation method is developed for a new 6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(tert-butyl)- 1,2-benzoquinone], including the stage of 3,5-di(tert-butyl)pyrocatechol aminoalkylation by Mannich reaction followed by oxidation. The molecular structure of one of its hydrolysis products, 4,6-di(tert-butyl)-2,3-dihydroxybenzaldehyde, is established by X-ray diffraction (XRD) analysis.     

Synthesis of Derivatives of of Δ2-Imidazolin-5-one and Imidazolidine Containing Residues of Sterically-hindered Phenols

1-Substituted 4-benzylidene-2-{-[3,5-di(tert-butyl)-4-hydroxyphenyl]vinyl}-4-benzylidene-²-imidazolin-5-ones have been synthesized by the interaction of azomethines and N-acylhydrazones (derivatives of 3,5-di(tert-butyl)-4-hydroxybenzaldehyde) with 4-benzylidene-2-methyloxazol-5-one. The acylation of 1,2-bis[3,5-di(tert-butyl)-4-hydroxybenzylideneamino]ethane with acid chlorides in acetonitrile in the presence of triethylamine leads to 1,3-diacyl-2-[3,5-di(tert-butyl)-4-hydroxyphenyl]imidazolidine.     

Visible-light-induced novel cyclization of 2-(2-(arylethynyl)benzylidene)-malononitrile derivatives with 2,6-di(tert-butyl)-4-methylphenol to bridged spirocyclic compounds

A green and highly efficient strategy for the preparation of bridged spirocyclic compounds via visiblelight-induced cyclization of 2-(2-(arylethynyl)benzylidene)malononitrile derivatives with 2,6-di(tertbutyl)-4-methylphenol(BHT) at room temperature was developed. The photoinduced radical reactions generated the corresponding products in good yields under simple and mild reaction conditions.     

Diastereoselective Radical Reactions Starting from Cyclic Iodohydrin Derivatives

The stereoselectivity of radical reactions using cyclic iodohydrins and 2-alkoxy iodides was investigated on a simple model system obtained from indene (see 1a ? d ). The low level of stereoselectivity inherent to this type of systems could neither be overcome by using large protective group on the O-atom of 1c nor by complexation with Lewis acids. However, starting from the free alcohol 1c , it was possible to obtain very high selectivities (trans/cis > 100:1) by forming an aluminium alkoxide derivative upon treatment with methylaluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) before running the radical reaction. Despite the high steric demand of these complexes, the reactions gave satisfactory yields even for the formation of C? C bonds.     

Reaction of 3,6-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2-benzoquinone with terminal alkylacetylenes in the presence of phosphorus trichloride

A reaction of 3,6-di(tert-butyl)-1,2-benzoquinone with alkynes in the presence of phosphorus trichloride leads to a predominant formation of 4-alkyl- and 4-haloalkyl-5,8-di(tert-butyl)-2,6-dichloro-2 H- benzo[e][1,2]oxaphosphinine 2-oxide. An ipso-substitution of the tert-butyl group at ortho-position to the oxygen atom of the benzophosphinine system with the formation of 4-alkyl-5- tert-butyl-2,8-dichloro-2 H-benzo[e][1,2]oxaphosphinine 2-oxide was the minor route of the reaction with alkylacetylenes. Molecular structures of 4-butyl-5,8-di( tert-butyl)-2,6-dichloro-2 H- benzo[e][1,2]oxaphosphinine 2-oxide and 5,8-di( tert-butyl)-2,6-dichloro-4-hexyl-2 H-benzo[e][1,2]oxaphosphinine 2-oxide were studied by X-ray analysis.     

Efficient Control of the Stereoselectivity in Reactions of 2-Oxy-Substituted Benzylic Radicals

The stereoselectivity in reactions of 2-oxy-substituted radicals of type B was investigated. As expected, minimization of allylic 1,3-strain was the major controlling factor. Under standard conditions, only a modest level of stereoselectivity was observed. E.g., deuteration of the benzylated radical (R¹ = benzyl) gave diastereoisomer ratios ≤ 2:1. Use of a bulky protective group on the O-atom (R¹ = (t-Bu)Ph₂Si) enhanced slightly the selectivity (ratio 4.1:1). However, a dramatic increase of the stereoselectivity (ratio 13:1) was obtained, when the reaction was performed with the free alcohol after treatment with bulky methylaluminium bis(phenoxide) derivatives (methyl-aluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) and methylaluminium bis(2,6-diphenylphenoxide) (MAPH)).     

Synthesis of 2-Substituted and 2,3-Disubstituted Quinazolin-4-ones Containing a Sterically Hindered Phenol Residue

A series of 2-substituted and 2,3-disubstituted quinazolin-4-ones containing a 3,5-di(tert-butyl)-4-hydroxyphenyl group has been synthesized. They were prepared by the condensation of carboxylic acid imino ester hydrochlorides containing the indicated fragment with ethyl anthranilate and also by the reaction of azomethines, N-acylhydrazones, or the 4-phenylthiosemicarbazone of 3,5-di(tert-butyl)-4-hydroxybenzaldehyde with 2-methyl-4H-2,1-benzoxazin-4-one.     

Benzylation of tetraalkylcalix[4]resorcinols

New amphiphilic benzylated calix[4]resorcinols were synthesized by the reaction of tetra-alkylcalix[4]resorcinols with 3,5-di(tert-butyl)-4-hydroxybenzyl acetate. The reaction pathway and the type of the products formed are determined by the structure of the alkyl substituent at the lower rim of tetraalkylcalix[4]resorcinols and the nature of acid used as a catalyst of the process. Self-organization of some synthesized compounds in nonpolar media was studied.     

Structure,synthesis, and voltammetric investigation of 1-(quinolin-2-yl)-2-(pyran-2-yl)ethane-1,2-dione derivatives

By the XRD analysis the structure was established of 1-(7,8-dimethyl-4-chloroquinolin-2-yl)-2-[3,5-di(tert-butyl)-6-oxo-6H-pyran-2-yl]ethane-1,2-dione formed as a result of the oxidation of 3,5-di(tert-butyl)-6-[(Z)-2-(quinolin-2-yl)-1-hydroxyethen-1-yl]pyran-2-ones. By the cyclic voltammetry the oxidation of 1-(quinolin-2-yl)-2-(pyran-2-yl)ethane-1,2-dione derivatives was shown to proceed in two stages.     

Intermediacy of Proton-Bound Dimers and Ion/Dipole Complexes in the Unimolecular Decompositions of Dialkyl-Peroxide Radical Cations: Evidence for a coupled proton and hydrogen-atom transfer

The unimolecular fragmentation reactions of the radical cations of diethyl, diisopropyl, dipropyl, isopropyl propyl, and di(tert-butyl) peroxide have been investigated by mass spectrometric and isotopic labeling techniques. Two competing pathways for unimolecular decomposition in the μs time regime (metastable ions) are observed: i) A combination of an α-C? C bond cleavage and a H migration gives rise to proton-bound dimers of two ketone or aldehyde molecules. ii) Ion/dipole complexes of alkyl cations and alkylperoxy radicals are generated by C–O bond cleavage. These complexes either exhibit direct losses of alkylperoxy radicals, or they rearrange via a coupled proton and H-atom transfer, this sequence of unprecedented isomerizations is completed by losses of alkyl radicals. Collisional activation experiments confirm that the ionic products of the latter process correspond to RR′C?OOH⁺; these ions can be regarded as protonated carbonyl oxides. In addition, we observe the elimination of alkenes leading to hydroperoxide radical cations and the expulsion of HO radicals. The latter process implies a C? C bond formation step between the two alkyl fragments leading to higher alkyl cations.     

A study on ester formylhydrazones

A series of ester formylhydrazones 2 were synthesized from the reaction of alkyl imidate hydrochlorides 1 with formylhydrazine. Treatment of 2 with hydrazine hydrate, ethyl carbazate and tert-butyl carbazate led to the formation of 3-alkyl-4-amino-, 3-alkyl-4-ethoxycarbonylamino- and 3-alkyl-4-tert-butoxycar-bonylamino-4H-1,2,4-triazoles 3–5 , respectively. Reaction of compounds 2 with formylhydrazine gave N,N'-diformylhydrazine 6 . Compounds 2 were reacted with 2,5-dimethoxytetrahydrofuran to afford 3-alkyl-4-(1H-pyrrol-1-yl)-4H-1,2,4-triazoles 8 .     

Carbon-13 spectra of some tetrahydropyridines. The structure of the tetrahydropyridines from 3,5-lutidine 1-oxide and mercaptans in acetic anhydride

The reaction of 3,5-lutidine 1-oxide ( 1 ) with t-butyl mereaptan in acetic anhydride, with or without triethylamine, was reinvestigated. There was obtained 2-t-butylthio-3,.5-lutidine as the major product, a small quantity of 3-(t-bulylthio)methyl-5-picoline, 1-acetyl-2,3-diacetoxy-3,5-dirnethyl-6-t-butylthio-1,2,3,6-tetrahydropyridine (which represents a structure revision) and l-acetyl-2,6-dihydroxy-3-t-butylthio-3,5-dimethyl-1,2,3,6-tetrahydropyridine. A similar reaction of 1 with 1-adamantyl mercaptan furnished 2-(l-adamantylthio)-3,5-lutidine and 1-acetyl-2,3-diacetoxy-3,5-dimethyl-6-(1-adamantylthio)-1,2,3,6-tetrahydropyridine. The structures of these new tetrahydropyridines were established primarily by carbon-13 nmr spectra.     

Absolute rate constants for the reactions between amino and alkyl radicals at 298 K

The absolute rate constants for the reactions of NH₂ radicals with ethyl, isopropyl, and t-butyl radicals have been measured at 298 K, using a flash photolysis–laser resonance absorption method. Radicals were generated by flashing ammonia in the presence of an olefin. A new measurement of the NH₂ extinction coefficient and oscillator strength at 597.73 nm was performed. The decay curves were simulated by adjusting the rate constants of both the reaction of NH₂ with the alkyl radical and the mutual interactions of alkyl radicals. The results are k(NH₂ + alkyl) = 2.5 (±0.5), 2.0 (±0.4), and 2.5 (±0.5) × 10¹⁰ M^?1·s^?1 for ethyl, isopropyl, and t-butyl radicals, respectively. The best simulations were obtained when taking k(alkyl + alkyl) = 1.2, 0.6, and 0.65 × 10¹⁰M^?1·s^?1 for ethyl, isopropyl, and t-butyl radicals, respectively, in good agreement with literature values.     

Radical polymerization of alkyl crotonates as 1,2-disubstituted ethylenes leading to thermally stable substituted polymethylene

Radical polymerization of several alkyl crotonates (RCr) was carried out in bulk or in benzene in the presence of radical initiators. Homopolymerization of RCr bearing bulky ester alkyl groups, e.g. tert-butyl (tBCr), 1-adamantyl (AdCr), and 3,5-dimethyl-1-adamantyl crotonate (DMAdCr) proceeded to give a polymer with molecular weight of several thousands despite of the steric hindrance and chain transfer by the presence of the β-methyl group, while the methyl and ethyl esters gave no polymer. The kinetics of the polymerization was examined in detail and absolute rate constants were evaluated by means of electron spin resonance spectroscopy. The propagation rate constants of RCr were 0.41–1.0 L/mol s, being much smaller than those of the corresponding methacrylates (530–570 L/mol s). The termination rate constants were also determined from the analyses of steady state and non-steady state polymerizations. Radical copolymerizations of AdCr (M₂) with several vinyl monomers (M₁) were carried out in bulk at 60°C and the rate constants for cross propagations were calculated to examine reactivities of the monomer and its polymer radical. The structure and thermal properties of the resulting poly (AdCr) were also investigated. Onset temperature of decomposition and glass transition temperature of poly(AdCr) were revealed to be much high as 302 and 234°C, respectively. © 1994 John Wiley & Sons, Inc.     

Copper (II) complexes of sterically hindered o-diphenol derivatives: synthesis, characterization and microbiological studies

Cu (II) complexes with the sterically hindered diphenol derivatives 3,5-di(tert-butyl)-1,2-benzenediol (I), 4,6-di(tert-butyl)-1,2,3-benzenetriol (II) and the sulfur-containing 4,6-di(tert-butyl)-3-(2-hydroxyethylsulfanyl)-1,2-benzenediol (III) and 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (IV) have been synthesized and characterized by elemental analysis, TG/DTA, FT-IR, ESR, XPS, XPD and conductivity measurements. Compounds I–III can coordinate in their singly deprotonated forms and act as bidentate ligands. These compounds yield Cu (II) complexes of the stoichiometry Cu(L)₂, which have square planar geometry (g_| > g_⊥ > g_e). Unlike them, compound IV behaves as a terdentate ligand, and its complex Cu(L^IV)₂ has distorted octahedral geometry. According to ESR data, only the Cu(L^II)₂ complex contains a very small amount of phenoxyl radicals. Antimicrobial activities of these ligands and their respective Cu (II) complexes have been determined with respect to Gram-positive and Gram-negative bacteria, as well as on yeasts. Their phytotoxic properties against Chlorella vulgaris 157 were also examined.     

Synthesis and study of electrochemical properties of the sterically hindered phenol derivatives and the corresponding radicals

1-(3,5-Di-tert-butyl-4-hydroxyphenyl)-2-arylbenzimidazoles were synthesized by the condensation of 2,6-di-tert-butyl-p-benzoquinone imine with aromatic aldehydes. 2-(3,5-Di-tert-butyl-4-hydroxybenzylidene) benzimidazoles were synthesized by the reaction of 2-aminobenzimidazole with 2,6-di-tert-butyl-4-hydroxybenzaldehyde. The substances were characterized by elemental analysis, IR and NMR spectra. The electrochemical reduction and oxidation of these compounds and phenoxy radicals derived from them was studied by cyclic voltammetry. The stability of the studied phenoxy radicals was confirmed by the electron spin resonance method.