Oxidation of aromatic amines with chromyl chloride-I : Oxidation of aromatic primary amines

The oxidation of aromatic primary amines with chromyl chloride in carbon tetrachloride or chloroform, results in the formation of intermediate solid adducts (Etard adducts) which, on hydrolysis, give azobenzenes(1), 1,4-benzoquinones(2),anilino-1,4-benzoquinones(3), 1,4-benzoquinone anils(4)and anilino-1,4-benzoquinone anils (5) in yields which depend on the position, nature and degree of substitution of the ring.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Addition reactions of nucleophiles to dibenzoylacetylene

Several enamine diones have been prepared through the nucleophilic addition of different amines to dibenzoylacetylene (DBA). Thus, the reaction of aniline, piperidine, o-aminophenol and N-phenylbenzylamine with DBA gave the corresponding 1:1 adducts namely, 1,4 - diphenyl - 2 - (N - phenylamino)but - 2 - ene -1,4 - dione (1), 1,4 - diphenyl - 2 - piperidinobut - 2 - ene - 1,4 - dione (2), 2 - (N - 2 - hydroxyphenylamino)1,4 - diphenylbut - 2 -ene - 1,4 - dione (3) and 1,4 - diphenyl - 2 - (N - phenylbenzylamino)but - 2 - ene - 1,4 - dione (4). UV absorption data reveal that the adducts 1 and 3, formed from aniline and o-aminophenol, respectively, are the E-isomers, arising through a trans-mode of addition whereas the adducts 2 and 4, formed from piperidine and N-phenyl-benzylamine are the Z-isomers, formed through a cis-mode of addition.The reaction of N-phenaeylaniline with DBA gave 2,3 - dibenzoyl - 1,4 - diphenylpyrrole (5), whereas the reaction of 1,8 - diaminonaphthalene with DBA gave a mixture of products consisting of 2 - benzoyl - 2 - phenacyl -2,3 - dihydroperimidine (11) and 2 - benzoylperimidine (12). The reaction of 2-aminopyridine with DBA gave a mixture of two 1:1-adducts, 2 - (2 - imino - 1(2H) - pyridyl) - 1,4 - diphenylbut - 2 - ene - 1,4 - dione (14) and 1,4 -diphenyl - 2 - (N - 2 - pyridylamino)but - 2 - ene - 1,4 - dione (15).     

Synthesis of N-tosyl-3,3,4-trisubstituted pyrrolidine derivatives starting from the Baylis-Hillman adducts via radical cyclization

N-Tosyl-3,3-disubstituted-4-vinylpyrrolidine derivatives 3a-c were synthesized via radical cyclization from the modified Baylis-Hillman adducts 2. The required starting materials 2a-c were prepared in moderate yields from the Baylis-Hillman adducts in three steps: (i) acetylation of the Baylis-Hillman adducts, (ii) S_N2′ reaction with tosylamide to prepare 1, and (iii) alkylation with 1,4-dibromo-2-butene.     

Quinones and quinone methides—IV: Dimerization reactions of 2-phenylmethyl-5-methoxy-1,4-benzoquinones

Base catalyzed dimerization of 2-(4-methoxyphenylmethyl)-5-methoxy-1,4-benzoquinone 6 yields as the chief product an unusual tetrahydroxanthen derivative 7a. The structure of 7a suggests that it is formed by combination of two molecules of the ortho-quinone methide tautomer of 6. Rearrangement of 7a yields the dihydro-oxepin derivative 15 and the indanspirocyclohexene derivatives 17 and 18a, all of which are formed as minor products in the dimerization of 6. In contrast to 6 related 2-(1-phenylethyl)-1,4-benzoquinones do not dimerize in basic media.     

Cyclic voltammetry and theoretical calculations of silyl-substituted 1,4-benzoquinones

Cyclic voltammograms of 2,3,5,6-tetrakis(trimethylsilyl)-1,4-benzoquinone (1a), 2,3,5,6-tetrakis(dimethylvinylsilyl)-1,4-benzoquinone (1b), 2,3,5,6-tetrakis(dimethylsilyl)-1,4-benzoquinone (1c), 4,4,6,6,10,10,12,12-octamethyl-4,6,10,12-tetrasilatricyclo[7.3.0.0^3,7]dodeca-1(9),3(7)-diene-2,8-dione (1d), and 5-t-butyl-2-(pentamethyldisilanyl)-1,4-benzoquinone (5h) showed that the first reduction step was reversible and that the second step was irreversible. The first half-wave reduction potentials of 1a, 1b, 1c, and 1d shifted negatively relative to 1,4-benzoquinone by −0.31, −0.24, −0.03, and −0.18 V, respectively. These results demonstrated that the electron-accepting ability of the chair-form quinones 1a and 1b was lower than that of the planar quinones 1c and 1d. The of 5h (−0.93 V vs. Ag/Ag⁺) was quite similar to that of 5-t-butyl-2-trimethylsilyl-1,4-benzoquinone (5a, −0.94 V). A cyclic voltammogram of dimethylsilylene-bridged 1,4-benzoquinone dimer 7 showed two kinds of (−0.76 and −0.94 V). The electrochemical behavior of 7 would be interpreted in terms of near-neighbor interactions between reduced and non-reduced quinone units. Theoretical calculations of the silyl-1,4-benzoquinones reproduced well the solid state structures of the compounds. Also, the computed vibrational frequencies of the silyl-1,4-benzoquinones were in good agreement with the IR absorption frequencies of the CO units in the compounds. The LUMO energy levels of the silyl-1,4-benzoquinones were quantitatively proportional to the .     

Chemistry of O-Benzoquinones and Masked O-Benzoquinones I. Diels-Alder Reactions of O-Benzoquinones with Dimethyl Acetylenedicarboxylate and Phenylacetylene

Diels-Alder reactions of six o-benzoquinones with dimethyl acetylenedicarboxylate has been examined. The yields of adducts vary with the natures of the o-benzoquinones, 3,4-Di-n-propyl-(1c), 3,6-di-n-propyl (1d). 3. 4-diallyl-(1e) and 3, 6-diallyl-o-benzoquinone (1f) are found to give bicyclic a-diketones exclusively without the formation of 1,4-dioxine derivatives, the yields ranging from 20 to 70%. In the case of 4, 5-dimethoxy-o-benzoquinone, dimethyl 4, 5-dimethoxyphthalate is produced in 42% yield, presumably derived from the decomposition of the corresponding initially formed α-diketone. 3, 6-Di-n-propyl-4, 5-dimethoxy-o-benzoquinone deteriorates without addition to dimethyl acetylenedicarboxylate upon heating. The additions of o-benzoquinones 1c , 1d and 1f to phenylacetylene are also studied. The yields of adducts, α-diketones, range from 23% to 82%.     

Studies on Quinones. XIX. Improved Synthesis of 2-Nitro-1,4-benzoquinone and its Reaction with Nucleophiles

Reaction of 2-nitro-1,4-benzoquinone (4), easily obtained by oxidation of 3 with MnO₂/HNO₃, with various nucleophiles affords the corresponding adducts in high yields.     

Novel porphyrin-quinazoline conjugates via the Diels-Alder reaction

Novel derivatives of meso-tetraphenylporphyrin with appended quinazoline moieties were synthesized, via the Diels-Alder reaction, between a 4-(porphyrinyl)pyrimidine ortho-quinodimethane and 1,4-benzoquinone, 1,4-naphthoquinone and N-(p-nitrophenyl)maleimide. The structure of one bis adduct was established by X-ray crystallography and mass spectrometry. We have unequivocally confirmed that the 2:1 adducts obtained from the reaction of pyrimidine-fused 3-sulfolenes with N-arylmaleimides have an open-chain structure and not a cyclooctapyrimidine structure, as previously published.     

Oxidation of lignin model compounds in water with dioxygen and hydrogen peroxide catalysed by metallophthalocyanines

Water-soluble metallophthalocyanines and metalloporphyrins were tested as catalysts for the aqueous oxidations of 3,4-dimethoxybenzyl alcohol (1), 4-hydroxy-3-methoxytoluene (3) and 3,4-dimethoxytoluene (8) with dioxygen and with hydrogen peroxide. Cobalt phthalocyaninetetra(sodium sulfonate) (CoPcTS) catalysed the reactions of dioxygen with 1 to form only 3,4-dimethoxybenzaldehyde (2) and with 3 to form 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dimethylbiphenyl (4) and other, unidentified products at 70–85 °C and pH ⩾ 8, while the other catalysts were inactive. The most active catalyst for the oxidations of 1, 3 and 8 with hydrogen peroxide was FePcTS in acidic solution: alcohol 1 produced aldehyde 2 and 2-hydroxymethyl-5-methoxy-1,4-benzoquinone; phenol 3 produced dimer 4, 3-methoxy-4-hydroxybenzyl alcohol and a dimer with one hydroxymethyl group; 3,4-dimethoxytoluene (8) produced 2-methyl-5-methoxy-1,4-benzoquinone. Cationic latex particles had little effect on the oxidations.     

Synthesis of new calix[4]pyrrole derivatives via 1,3-dipolar cycloadditions

Octamethylcalix[4]pyrrole-2-carbaldehyde 1 and 3-(octamethylcalix[4]pyrrol-2-yl)propenal 5 were used as precursors of azomethine ylides, which were trapped in situ with a range of dipolarophiles, such as 1,4-benzoquinone, 1,4-naphthoquinone, and fumaronitrile. Aldehyde 1 showed very low reactivity but the azomethine ylide generated from the reaction of aldehyde 5 with N-methylglycine could be trapped with those dipolarophiles to afford new β-substituted octamethylcalix[4]pyrrole derivatives in moderate yields. The resulting cycloadducts show high affinity constants for fluoride and acetate anions; compounds 7 and 8 display sharp changes in color in the presence of these anions.     

Anomalous behavior in the two-step reduction of quinones in acetonitrile

The electrochemical reduction of eight quinones, 9,10-anthraquinone (1), duroquinone (2), 2,6-di-tert-butyl-1,4-benzoquinone (3), 2,6-dimethoxy-1,4-benzoquinone (4), 9,10-phenanthrenequinone (5), tetrachloro-1,2-benzoquinone (6), tetrabromo-1,2-benzoquinone (7) and 3,5-di-tert-butyl-1,2-benzoquinone (8), have been studied in acetonitrile. In every case it was found that cyclic voltammograms differed in significant ways from those expected for simple stepwise reduction of the quinone to its radical anion and dianion. The various types of deviations for the eight quinones have been cataloged and some speculation is offered concerning their origins.     

Oxidative free radical reactions between 2-amino-1,4-benzoquinones and carbonyl compounds

The manganese(III) initiated oxidative free radical reactions of 2-amino-1,4-benzoquinone are described. The free radical reaction of 5,6-dimethyl-2-methylamino-1,4-benzoquinone (1) provides a novel method for the synthesis of indole-4,7-dione and indole-2,4,7-trione. High chemoselectivity was observed in different solvents. The regioselectivity of this reaction was also studied with 5-methyl-2-methylamino-1,4-benzoquinone (19). In most cases, indole-4,7-diones 20 and 21 were produced in high regioselectivity.     

The reaction of α-phenethyl radicals with 1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone

The absolute rate constant for 1,4-benzoquinone (BQ) irreversibly trapping α-phenethyl radicals (3) has been determined as 4.4×10⁶ M⁻¹ s⁻¹ at 43 °C using acyclic cis azoalkane 9c as a radical precursor. These reactants afford the hydroquinone mono ether 4 at 30 °C but a mixture of products at elevated temperature. 2,6-Di-tert-butyl-1,4-benzoquinone (DTBQ) also reacts with 3 but the cyclohexadienone products are thermally labile.     

Aza-Morita-Baylis-Hillman reactions of N-(benzylidene)polyfluoroanilines with methyl acrylate and acrylonitrile

Aza-Morita-Baylis-Hillman reactions of N-(benzylidene)polyfluoroanilines 1 with methyl acrylate or acrylonitrile were studied. It was found that Lewis base, solvent and reaction temperature can significantly affect the reaction. Using 3-hydroxyquinuclidine (3-HQD) as a Lewis base in the reactions of 1 with methyl acrylate in DMF, the normal aza-Morita-Baylis-Hillman adducts 3 were formed in moderate to excellent yields. For the reactions of 1 with acrylonitrile, 1,4-diazabicyclo[2.2.2]octane (DABCO) is the best Lewis base giving the corresponding aza-Morita-Baylis-Hillman adducts 4 as the sole product in good to moderate yield. However, upon treatment of 1 with acrolein 2c, the corresponding reaction did not occur even in the presence of a variety of catalysts.     

Transformations of S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones and photochemical properties of reaction products

For the first time 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were prepared by the reactions of 3-alkylthio-5,7-dimethyl-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-imidazo[4,5-e]-1,2,4-triazin-6(4H)-ones with 3,5-di-tert-butyl-1,2-benzoquinone 1 and 4,6-di-tert-butyl-3-nitro-1,2-benzoquinone 2, respectively. Photochemical transformations of compounds 9 and 10a as well as products of its photooxygenation involving singlet oxygen under UV irradiation: urea 16, isomeric 1,3-dimethyl-4,5-diphenylimidazolidin-2-ones 17 and 17′, and compound 18 were studied by the spectral-kinetic method. Data on the absorption and fluorescence properties of synthesized compounds and their photoproducts were obtained.     

Conversion of isomeric 2:3 adducts (aminoacid-formaldehyde) to N-acyl-pseudoprolines derivatives

Reaction of acyl chlorides or acid anhydrides with isomeric 2:3 adducts derived from condensation of l-serine (1a), l-threonine (1b) and l-cysteine (1c) methyl esters with formaldehyde afforded N-acyl-pseudoprolines 7-19 in various yields. These 2:3 adducts can be considered as synthetic equivalents of oxaproline and thiaproline moieties. The present work revealed the versatile behaviour of the two 2:3 adducts as a consequence of the ring-chain tautomerism occurring in the five- and/or seven-membered rings.     

Synthesis of benzoquinone derivatives containing benzotriazole fragments

2,3,5,6-Tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone was synthesized in 85% yield by reaction of 2,3,5,6-tetrachloro-1,4-benzoquinone with 1H-benzotriazole in pyridine at room temperature. Treatment of 2,3,5,6-tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone with piperidine, ω-amino acids, and aromatic amines gave the corresponding 2,5-diamino-3,6-bis(1H-benzotriazol-1-yl)-1,4-benzoquinones.     

Use of bis-aminoalcohol benzoquinones and dihydroxybenzoquinones in the formation of mono and polymeric structures of diorganotin(IV) derivatives

Reaction of three hexadentate ligands (L1-L3) derived from 1,4-benzoquinone bis(aminoalcohols) with diorganotin oxides (R₂Sn-O)_n (with R = Me, nBu, Ph) in 1:2 stoichiometric proportions lead to the formation of dinuclear tin compounds of the composition [(R₂Sn)₂(L)], wherein the five-coordinate metal centers are embedded in distorted trigonal-bipyramidal polyhedra. X-ray diffraction analysis revealed that diorganotin complexes carrying n-butyl groups tend to associate further through intermolecular O?Sn interactions to give 1D polymeric chains, while diphenyltin analogues tend to be monomeric. On the other hand, using 2,5-dihydroxy-3,6-dichloro-1,4-benzoquinone as ligand (L4) in 1:1 reactions with the diorganotin oxide derivatives, 1D polymeric complexes of the composition [R₂Sn(L4)(DMSO)]_n with seven-coordinate metal centers in distorted pentagonal-bipyramidal coordination polyhedra were obtained. In this case, the presence of different substituents attached to the tin atoms (Me, nBu, Ph) had no influence on the molecular composition of the products, but on the conformation of the polymeric chain, which was either planar (R = Me), slightly distorted from planarity (R = nBu) or ondulated (R = Ph).     

Comparison of preparation methods of N-arylsulfinyl-1,4-benzoquinone monoimines

Advantages and shortcomings were discussed of three procedures for preparation N-arylsulfinyl-1,4-benzoquinone imines: the reaction of arenesulfenyl chlorides with 1,4-benzoquinone oximes, the oxidation of N-arylthio-1,4-benzoquinone imines, and the reaction of arylsulfinyl chlorides with p-aminophenols followed by oxidation. A series of new N-arylsulfinyl-1,4-benzoquinone imines was obtained.