Synthesis of functionalized p-dihydrobenzoquinones and p-benzoquinones based on [3+3] cyclizations of 1,3-bis-silyl enol ethers

Functionalized mono-protected p-dihydrobenzoquinones were prepared by [3+3] cyclization of 1,3-bis-silyl enol ethers with 2-acyloxy-3-(silyloxy)alk-2-en-1-ones. Deprotection and oxidation of the products afforded the corresponding p-benzoquinones.     

Electroanalytical study of isomeric trifluoromethyl-nitrosobenzene intermediates

The relative lifetimes of the o-, m- and p-trifluoromethylnitrosobenzene anion radicals produced in the electroreduction of the corresponding nitro compounds in N,N-dimethylformamide are compared. Potential step experiments coupled with cyclic voltammetry facilitate the comparison. The fate of the nitroso species is discussed in relation to the results of experiments in which o-, m- and p-trifluoromethylnitrobenzene were mass electrolyzed and the products spectrophotometrically identified.     

The oxidation of hydrazine derivatives with 4-phenyl-1,2,4-triazoline-3,5-dione

The oxidation of benzophenone hydrazone with 4-phenyl-1,2,4-triazoline-3,5-dione (PTD) yields benzophenone azine which is also formed from the reaction of the hydrazone with the ylid obtained from diphenyldiazomethane and PTD; the ylid forms a stable addition product with ethanol. With PTD, carbohydrazides are converted to 1,2-diacylhydrazines and small amounts of the corresponding azides; in contrast, p-toluenesulfonylhydrazine yields p-toluenesulfinic acid, isolated as its adduct with PTD, 1-(p-toluenesulfonyl)-4-phenylurazole. Possible mechanisms to rationalize the formation of these products are discussed.     

Application of ionic liquids for extraction and synthesis of organosulfur compounds

We consider the possible application of pyridinium ionic liquids to desulfurize hydrocarbon raw products and to transform the extracted toxic admixtures into promising sulfur compounds. Anodic oxidation of the extracted thiols as well as oxidation in the presence of electron mediators (N,N,N′,N′-tetramethyl-1,4-phenylenediamine, tri-p-bromophenylamine, and tri-p-tolylamine) leads to the corresponding disulfides.     

Asymmetric synthesis of 3-substituted 8-hydroxy-3,4-dihydroisocoumarins from (S)-4-isopropyl-2-(2-methoxy-6-methylphenyl)oxazoline

Reaction of the laterally lithiated (S)-4-isopropyl-2-(2-methoxy-6-methylphenyl)oxazoline with p-tolualdehyde gave an inseparable mixture of the addition products in low diastereoselectivity. However, the (S,S)-product cyclized to the corresponding 3,4-dihydroisocoumarin faster than the (S,R)-product on silica gel, which allowed to be produced both enantiomers of 8-methoxy-3-(p-tolyl)-3,4-dihydroisocoumarin in moderate to good optical purity [S-enantiomer: 75% ee; R-enantiomer: 96% ee]. This procedure was applied to the short-step synthesis of optically active 3,4-dihydroisocoumarin natural products such as (R)-8-hydroxy-3-(1-tridecyl)-3,4-dihydroisocoumarin and (R)-phyllodulcin.     

Peroxy esters—III: Acid-catalyzed reaction of 4-hydroperoxy-2,5- cyclohexadienones and their derivatives

Acid-treatment of 4-hydroperoxy-2,5-cyclohexadienones (peroxy-p-quinols) and their acetates leads to the corresponding quinoxy cations through a protonation at the peroxy group, giving rise to different types of products depending on the structure of the peroxy esters. 2,4,6-Trialkyl-p-quinoxy cations undergo a rearrangement with ring opening to give 4-oxa-2-cyclopentenone derivatives, except for p-quinoxy cations with t-butyl or benzyl groups at the 4-position where 2,6-di-t-butyl-p-benzoquinone is exclusively obtained. p-Quinoxy cations with aromatic substituents at the 4-position undergo migration of this substituent to the cationic oxygen. In the case of peroxy-p-quinols (even peroxy-p-naphthoquinols) with 4-aryl substituents the protonation occurs at either O atom of the peroxy bond. Peroxy-p-quinols and their acetates with an unhindered dienone system are quite stable towards acid treatment, probably due to a competitive protonation of the peroxy and the dienone CO group. In solvents containing an oxygen function the reaction proceeds slowly.     

Isomerization and functionalization of 2:1 Diels–Alder adducts of cyclopentadiene and p-benzoquinone: Applications to polycycles via ring-closing metathesis and ring-opening metathesis as key steps

Five stereochemically different 2:1 Diels–Alder adducts were prepared starting with cyclopentadiene and p-benzoquinone. Separately, these adducts were treated with an excess amount of base and allyl bromide to deliver two different tetra-allylated products. These allyl derivatives gave the corresponding mono-propellane derivatives on metathesis sequence. Five Diels–Alder adducts on treatment with Grubbs ruthenium catalysts delivered the corresponding mono- and di-ring-opened metathesis products. Structures of three functionalized adducts were determined by single-crystal X-ray diffraction studies.     

pTSA-catalyzed condensation of xylenols and aldehydes under solvent-free conditions: One-pot synthesis of 9H-xanthene or bisphenol derivatives

A simple and efficient procedure for the synthesis of 9H-xanthene or bisphenol derivatives has been developed by one-pot condensation of xylenols with aromatic aldehydes in the presence of p-toluenesulfonic acid (pTSA) as a catalyst under solvent-free conditions at 100 °C. It is noteworthy that the condensation reaction of 3,5-xylenol with aldehydes produces 9H-xanthene derivatives, while the reaction with other xylenols leads to the corresponding bisphenol derivatives. Different types of aromatic aldehydes are used in the reaction and in every case the products were obtained in good to excellent yields. The structures of these compounds were established on the basis of IR, ¹H NMR, ¹³C NMR and CHN data.     

DDQ-promoted direct C–H amination of ethers with N-alkoxyamides under visible-light irradiation and metal-free conditions

A C(sp³)–N bond forming reaction between N-alkoxyamides and simple ethers has been developed. In the presence of commercially available 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), a variety of N-methoxyamides and ethers undergo this transformation smoothly to deliver the corresponding products in good yields under visible-light irradiation and metal-free conditions at room temperature.     

Configurationally and conformationally homogeneous cyclic n-aryl sulfimides—III : Stereochemistry of rearrangement

Configurationally and conformationally homogeneous thiane- and trans- and cis-1-thiadecalin-1-N-p-chlorophenyl imides were rearranged to the corresponding 2-(2'-amino-5'-chlorophenyl)-sulfides and the configurations of the products were assigned by ^1H-NMR spectroscopy. If sterically unhindered, rearrangements proceeded with a high degree (95%) of stereospecifity: sulfimides with equatorial S-N-bond gave rearranged products with axial, sulfimides with axial S-N-bond gave rearranged products with equatorial aryl substituent. The proposed concerted mechanism via a cyclic transition state is supported by these results.     

Synthesis and some transformations of polybrominated quinone diazides

The reduction of polybrominated o- and p-nitrophenols with granular tin in concentrated aqueous HCl gave polybrominated aminophenols which were diazotized with sodium nitrite in concentrated sulfuric acid at 0°C to obtain polybrominated o- and p-quinone diazides. Their thermolysis with elimination of nitrogen generated ketocarbenes which reacted with acetylacetone to form insertion products at the activated methylene group. Ketocarbenes generated from o-quinone diazides reacted with typical dipolarophiles such as acetonitrile, benzonitrile, styrene, and phenylacetylene to afford the corresponding [3 + 2]-cycloaddition products.     

Products of photoreduction of 9,10-phenanthrenequinone in the presence of N,N-dimethylanilines and polymethylbenzenes

Photoreduction of 9,10-phenanthrenequinone (PQ) in the presence of p-substituted N,N-dimethylanilines and polymethylbenzenes affords corresponding phenolethers as primary products. In the subsequent process shielded from light, phenolethers, which were formed by photoreaction of PQ with N,N-dimethylanilines, were quantitatively converted to give corresponding ketols. Phenolethers of 9,10-phenanthrenequinone and polymethylbenzenes are rearranged only under irradiation and in the presence of second molecule of PQ to form ketols. Stability of phenolethers is determined by redox properties and structure of hydrogen donors.     

Hydroxylation of phenol over ts-2, a titanium silicate molecular sieve

The influence of different process parameters on the hydroxylation of phenol with H₂O₂ over the titanium silicate molecular sieve TS-2 has been investigated. Apart from the primary products vis., p- and o-dihydroxybenzenes, the corresponding quinones are also formed. Higher Ti contents in the catalyst (TS-2) and higher catalyst concentrations lower the formation of the secondary oxidation products. Solvents have an influence on the relative amounts of the two dihydroxybenzenes in the product. H₂O₂ efficiency of up to 74% is obtainable at ∼ 28% phenol conversion to dihydroxybenzenes.     

Novel capto-dative (Z,E)-2-(alkylthio)alk-2-en-4-ynals: synthesis and heterocyclization

An efficient synthesis of new (Z,E)-2-(alkylthio)alk-2-en-4-ynals by aldol condensation reaction of ynals with (alkylthio)-acetaldehydes using NaOH/DMF system has been developed.The reaction of these products with N,N-diphenylethylene-diamine and p-tosylmethyl isocyanide proceeds at the carbonyl group to form the corresponding imidazolidine and oxazole derivatives.     

Direct N- and C-alkenylation of nitrogen-containing heterocycles with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with N-lithio nitrogen-containing heterocycles gave N-alkenylated products in moderate to good yields. Also, the reaction of C-lithio indoles, which were generated from N-protected indoles, with magnesium alkylidene carbenoids gave C-2 or C-3 alkenylated products, corresponding to the protective group. The intermediate of these reactions were found to be the alkenyl anion, which could be trapped with electrophiles to give the heterocycles having fully substituted alkenes.     

Active monomeric nucleotide intermediate in the oligonucleotide synthesis

The interaction of 3′ - O - acetylthymidine - 5′ - phosphate (pT-Ac) and p - nitrophenylphosphate (pPhNO₂) with triisopropylbenzenesulphonyl chloride (TPS) in pyridine was studied by the pulsed NMR spectroscopy on ³¹P nuclei. The esters investigated were shown to convert to the corresponding disubstituted pyrophosphates, trisubstituted tripolyphosphates and compounds showing a singlet displaced 5–8 ppm from the original ester. The latter are the main final products of the interaction of nucleotide and pPhNO₂ with TPS. The investigation of the chemical conversion of a pT-Ac derivative with a 5·1 ppm shift showed that this product is a powerful phosphorylating reagent. It was shown that this active derivative contains one P atom in accordance with the structure of monomeric metaphosphoric acid ester proposed by Todd for these compounds. The reaction of monomeric metaphosphate with 5′-O-tritylthymidine results information of a compound, containing stoichiometric amounts of pT-Ac and 5′ - O - tritylthymidilyl - (3′ → 5′) - 3′ - O - acetylthymidine residues. This compound was identified as a trisubstituted P¹ - 5′ - O - trityl - P¹ - P² -bis -(3′ - O - acetylthymidine) - pyrophosph     

New synthetic approach to α-fluoro-β-arylvinyl sulfones and their application in Diels-Alder reactions

A new pathway towards α-fluoro-β-arylvinyl sulfones was elaborated. The reaction of β-bromo-β-fluorostyrenes with sodium 4-methylphenylsulfinate proceeds with maximum 94:6 stereoselectivity and 72-90% yields. The formed α-fluoro-β-arylvinyl sulfones were found to be good dienophiles for Diels-Alder reactions with simple 1,3-dienes. From corresponding (E)-configured dienophiles and cyclopentadiene, cycloadducts bearing the fluorine substituent in exo-position were formed predominantly, while with diphenylisobenzofuran the products with endo-orientation of the fluorine were obtained as the major products. From these cycloadducts, as a proof of principle, p-toluenesulfinic acid was eliminated to give 2-fluoro-3-(4-nitrophenyl)norbornadiene, the formal [4+2]-cycloadduct of cyclopentadiene and 1-fluoro-2-(4-nitrophenyl)acetylene, or the corresponding diphenylisobenzofuran cycloadducts, respectively. This reaction was not successful when other β-hydrogen atoms are accessible for elimination.     

Photo-Fries rearrangement of N-arylsulfonamides to aminoaryl sulfone derivatives

Photochemical reaction of variously substituted p-toluenesulfonanilides was studied. The reaction gives rearranged products, o- and p-amino-substituted diaryl sulfones with the combined yields of 38-72%: the p-isomer is more favored over the o-isomer with the selectivity ratio of 1.1-4.3 depending on the substituents. N-Alkylation of the sulfonanilides increases the yields of the rearranged products, and e-withdrawing substituents on the N-phenyl ring does not lower the yields drastically. This study provides simple methodology for the synthesis of o- and p-aminoaryl sulfones which are otherwise not easily accessible.     

Redox-neutral C–H cyanation of tetrahydroisoquinolines under photoredox catalysis

Redox-neutral cyanation of C–H bond adjacent to a nitrogen atom was achieved by using the combination of a photoredox catalyst and p-toluenesulfonyl cyanide. The reaction of tetrahydroisoquinolines proceeded smoothly, affording the corresponding cyanated products selectively in good to high yield. Although the reaction rate became slower in the case of the substrates having electron-withdrawing groups, high yields were achieved by elongating the reaction time. Although the yields were only moderate, the reaction conditions were also applicable to N,N-dialkylanilines.     

Solubility of metal oxides in molten equimolar KBr-NaBr mixture at 973 K

Solubility products (pK _s,MO, molality) are measured by potentiometric titration with a Pt(O₂)|ZrO₂(Y₂O₃) oxygen electrode in the molten KBr-NaBr equimolar mixture at 973 K for the following oxides: CaO (5.00 ± 0.3), MnO (7.85 ± 0.3), NiO (9.72 ± 0.04), PbO (5.20 ± 0.3), and SrO (3.81 ± 0.3). The correlation between pK _s,MeO and the polarization of the corresponding cations by Goldschmidt is obtained.