Tele- versus normal substitution in the reaction of 1,4-dialkyl-2,3-dinitronaphthalenes with sodium arenethiolates in dmso

1,4-Dimethyl-2,3-dinitronaphthalene (1) reacts with sodium arenethiolates in DMSO to give 2-arylthio-1, 4-dimethyl-3-nitronaphthalene (3) [normal substitution product (NSP)] and 1-arylthiomethyl-4-methyl-3-nitronaphthalene (5) [tele-substitution product (TSP)]. The percentage of TSP is found to increase with the enhancement of the reaction temperature, the presence of electron-withdrawing substituents in the arenethiolate; the increase of steric hindrance in the nucleophile, and the substitution of two Et for two Me groups in 1. A mechanism, involving a partial tautomerization of 1 into 2,3-dinitro-4-methyl-1-methylene-1,2-dihydronaphthalene (7) followed by attack of the nucleophile on this tautomeric form, is suggested to account for the formation of TSP. The analogous reactions on 1,4-dimethyl-2,3-dinitrobenzene and 5,8-dimethyl- and 5,8-diethyl-6,7-dinitro-1,2,3,4-tetrahydronaphthalene yield only NSPs. Some double bonds localization together with steric compression in the congested naphthalene derivative are suggested to play an important role in driving the reaction along the tele-substitution pathway.     

A synthetic entry into the 2- and 3-substituted-methyl 2,3-dihydro-1,4-benzoxazine series

Nmr spectroscopy has been used to demonstrate that the reported preparation of supposed 3-bromomethyl-2,3-dihydro-1,4-benzoxazine ( 3 ) is in error, the product of the reaction being in reality a monocyclic compound, 4 . An alternative entry to the 3-substituted series is described in the synthesis of the 3-hydroxymethyl derivative, 10 , the structure of which was established by nmr and mass spectroscopy. The previous assignment of structure to 2-carbethoxy-2,3-dihydro-1,4-benzoxazine, prepared by an ambiguous route, and to compounds derived from this ester, is shown to be correct.     

Reactions of palladium (II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4-DI(p-methoxyphenyl)-2,3-dimethyl- 1,4 - diazabutadiene

The reactions of palladium(II) chloride with 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene and 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene are described. With 1,4 - diphenyl - 2,3 - dimethyl - 1,4 - diazabutadiene diimine fission is produced, giving rise to a product identified by elemental analysis, IR and Raman spectra, and X-ray diffraction, as trans-dichlorobis(aniline) palladium(II). The complex is soluble in dimethylformamide and crystallizes with two molecules of solvent. The substance crystallizes in the monoclinic space group P2₁/n. The X-ray data were refined to R = 0.047 and R_w = 0.046. Final distances are PdN = 2.060(5)Åand PdC1 = 2.299(2)Å. There are two bifurcated intermolecular NH ... C1 and CH... C1 hydrogen bonds which, together with one more intermolecular hydrogen bond NH... O, are responsible for the packing of the molecules. However, when 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was treated with palladium chloride under the same conditions cis - dichloro - 1,4 - di(p - methoxyphenyl) - 2,3 - dimethyl - 1,4 - diazabutadiene was formed, as deduced from elemental analysis, and IR and Raman spectra.     

A study of the photochemically induced electron-transfer reactions between pyridinedicarbonitriles and primary and secondary aliphatic amines

A study on the photochemically induced electron-transfer from primary and secondary aliphatic amines as donors to pyridinedicarbonitriles as the acceptor is reported. A comparison between the substitution positions and the spin density distributions, obtained via theoretical calculations using the 6-31+G basis set, shows some discrepancies, and forms the basis of a hypothesis on the mechanism of the reaction.     

Aromatic nucleophilic substitution reactions in the naphthalene series. A kinetic study of the reaction between 2,3-dinitronaphtahlene and piperidine in benzene

The title reaction shows a curvilinear dependence (downward curvature) of the overall third order rate constant (second order in piperidine) on amine concentration. This and other experimental results have been rationalized with a stepwise mechanism of the anomalous addition-elimination (AEa) type involving a change in rate-determining step within the kinetically significant addition process.     

Five-membered 2,3-dioxo heterocycles: LXXII. Recyclization of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates by the action of aliphatic amines

Reactions of isopropyl 2-(1-aryl-4,5-dioxo-2-phenyl-4,5-dihydro-1H-pyrrol-3-yl)-2-oxoacetates with alkylamines involve pyrroledione-pyrroledione recyclization with formation of isopropyl 1-aryl-2-hydroxy-4,5-dioxo-3-[phenyl(alkylamino)methylidene]pyrrolidine-2-carboxylates.     

Studies on the reactivity of aryliodonium ylides of 2-hydroxy-1,4-naphthoquinone: reactions with amines

Aryliodonium ylides of 2-hydroxy-1,4-naphthoquinone react with amines in refluxing dichloromethane to afford good yields of indanedione 2-carboxamides 5, through a ring-contraction and alpha,alpha'-dioxoketene formation reaction. These amides exist in solution in an unusual enol-amide form. In contrast, the same reactants in a copper-catalyzed reaction afford arylamines and 3-iodo-4-hydroxy-1,2-naphthoquinone.     

Unexpected reduction of ethyl 3-phenylquinoxaline-2- carboxylate 1,4-di-N-oxide derivatives by amines

The unexpected tendency of amines and functionalized hydrazines to reduce ethyl 3-phenylquinoxaline-2-carboxylate 1,4-di-N-oxide (1) to afford a quinoxaline 1c and mono-oxide quinoxalines 1a and 1b is described. The experimental conditions were standardized to the use of two equivalents of amine in ethanol under reflux for two hours,with the aim of studying the distinct reductive profiles of the amines and the chemoselectivity of the process. With the exception of hydrazine hydrate, which reduced compound 1 to a 3-phenyl-2-quinoxalinecarbohydrazide derivative, the amines only acted as reducing agents.     

Reactivity of 2-formylphenylboronic acid toward secondary aromatic amines in amination-reduction reactions

The synthesis of 2-(arylaminomethyl)phenylboronic acid via an amination-reduction reaction has been investigated within a model system comprising 2-formylphenylboronic acid and N-ethylaniline. Adoption of the appropriate reaction conditions influences the reactivity of 2-formylphenylboronic acid, enabling efficient synthesis of so-far unobtainable 2-(arylaminomethyl)phenylboronic compounds. The first crystal structure of the aromatic amine derivative has been determined and described.     

Gas-phase reactions of 1,4-benzodioxan, 2,3-dihydrobenzofuran,and 2,3-benzofuran with OH radicals and O3

The kinetics of the gas-phase reactions of 1,4-benzodioxan, 2,3-dihydrobenzofuran, and 2,3-benzofuran with OH radicals and O₃ have been studied at 298 ± 2 K and atmospheric pressure of air and the products have also been investigated. 1,4-Benzodioxan and 2,3-dihydrobenzofuran were chosen as volatile model compounds for dibenzo-p-dioxin and dibenzofuran, respectively. The rate constants, or upper limits thereof, for the O₃ reactions were (in cm³ molecule^?1 s^?1 units): 1,4-benzodioxan, <1.2 × 10^?20; 2,3-dihydrobenzofuran, <1 × 10^?19; and 2,3-benzofuran, (1.83 ± 0.21) × 10^?18. Using a relative rate method, the rate constants for the OH radical reactions (in cm³ molecule^?1 s^?1 units) were: 1,4-dibenzodioxan, (2.52 ± 0.38) × 10^?11; 2,3-dihydrobenzofuran, (3.66 ± 0.56) × 10^?11; and 2,3-benzofuran, (3.73 ± 0.74) × 10^?11. Salicylaldehyde was observed as a product of the OH radical-initiated and O₃ reactions of 2,3-benzofuran, with measured formation yields of 0.26 ± 0.05 and 0.13 ± 0.07, respectively.     

Amphoteric 2-(sulfonylamino)benzaldehydes,secondary amines and isocyanides in the multicomponent synthesis of elusive N-alkyl-2,3-diaminoindoles

A novel interrupted Ugi reaction between ortho-sulfonylaminated aryl aldehydes, secondary amines, and isocyanides affords in good to high yields N-alkyl-2,3-diaminoindoles, providing access to a so far unexplored area of the indole chemical space. With only one single chemical operation, this novel reaction affords a broad gamma of substituted 2,3-diaminoindoles with five points of diversity. The success of this novel multicomponent transformation lies in presence of the amphoteric sulfonylamino group, which sequentially acts as a Brønsted acids and as a nucleophile the lack of need for additional catalysts and the high atom economy, with the loss of only one molecule of water, renders this approach a very effective one.     

Synthesis of methyl carbamates from primary aliphatic amines and dimethyl carbonate in supercritical CO2: effects of pressure and cosolvents and chemoselectivity

[reaction: see text] At 130 degrees C, in the presence of CO2 (5-200 bar), primary aliphatic amines react with dimethyl carbonate (MeOCO2Me, DMC) to yield methyl carbamates (RNHCO2Me) and N-methylation side-products (RNHMe and RNMe2). The pressure of CO2 largely influences both the reaction conversion and the selectivity toward urethanes: in general, conversion goes through a maximum (70-80%) in the midrange (40 bar) and drops at lower and higher pressures, whereas selectivity is continuously improved (from 50% up to 90%) by an increase of the pressure. This is explained by the multiple role of CO2 in (i) the acid/base equilibrium with aliphatic amines, (ii) the reactivity/solubility of RNHCO2- nucleophiles with/in DMC, and (iii) the inhibition of competitive N-methylation reaction of the substrates. Cosolvents also affect the reaction: in particular, a drop in selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2- moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)n NH2, X = NH2, OH; n = 1, 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding methyl carbamates [XC6H4(CH2)n NHCO2Me] in 39-65% isolated yields.     

Electron-impact fragmentation of some secondary aliphatic nitramines. Migration of the nitro group in heterocyclic nitramines

The mass spectra of a series of nitramines, including the explosives RDX and HMX, are reported. The nature of the major fragment ions is established by labeling with ¹⁵N or¹³C and by high resolution mass spectrometry. Electron-impact-induced fragmentation pathways including the migration of the nitro group in the heterocyclic nitramines, RDX and HMX, are postulated.     

Univocal syntheses of 2- and 3-hydroxymethyl-2,3-dihydro[1,4]dioxino[2,3-b]pyridine enantiomers

The enantiomers of 2- and 3-hydroxymethyl substituted 2,3-dihydro[1,4]dioxino[2,3-b]pyridine 1 and 2, important chiral building blocks for the preparation of several biologically active compounds, were synthesized. (S)- and (R)-1 were obtained from either one or both the enantiomers of benzylglycerol, while (S)- and (R)-2 were obtained from (R)- and (S)-isopropylideneglycerol, respectively. The novel efficient synthetic strategies, which do not follow routes already reported for the corresponding racemates, ensure very high regioselectivity and maintenance of the enantiomeric purity of the starting materials. The enantiomeric composition of the title compounds was determined by chiral HPLC or NMR. The key intermediate in the synthesis of non-racemic 1, namely 1-benzyl-2-mesyl-3-tritylglycerol, is a new high melting chiral C₃ synthon, worth considering for its stability, versatility, easy isolation by simple crystallization and, potential of configuration inversion through a simple one-pot reaction sequence.     

Lewis acid-promoted three-component reactions of propargylic alcohols with 2-butynedioates and secondary amines

We report herein a three-component reaction of propargylic alcohols with 2-butynedioates and secondary amines, which furnished functionalized dihydroazepines. In the cases where benzylmethylamine and benzyl-i-propylamine were used as the secondary amine, the reaction afforded 2,5-dihydro-1H-pyrroles and 2,3-dihydro-1H-pyrroles, respectively, as the major product along with the desired dihydroazepines. The reaction mode depends on the electronic and steric effect of the substitutents on the secondary amines used. A tentative mechanism for this cascade process is postulated. The key intermediate is ascribed to 1,3,4-pentatrien-1-amine, which is formed by trapping the in situ generating allenic carbocation with enamine. Because of the reactivity of 1,3,4-pentatrien-1-amine formed, different products were thus formed.     

Polyterephthalates of 2,3-disubstituted butanediols-1,4: Effect of aliphatic substituents on Tg and Tm of the polyesters

Poly(2,3-dialkylbutanediol-1,4 terephthalates) with the alkyl substituents CH₃, C₂H₅, n-C₃H₇, iso-C₃H₇, n-C₄H₉, and n-C₁₀H₂₁, andn-C₁₆H₃₃ were synthesized from the corresponding 2,3-dialkylbutanediols-1,4 and dimethyl terephthalate or terephthaloyl chloride. The substituents of the butanediol-1,4 portion of the polyterephthalates influence the ¹³C NMR chemical shifts of the carbon atoms near the branching site, the glass transition (T_g), and the crystallizability. Small alkyl substituents do not change the T_g of the polymers, whereas bulky substituents such as the isopropyl group increase the T_g and long normal alkyl groups as substituents decrease the T_g of the polymers. Crystallinity in these polyterephthalates was found only with CH₃ and C₁₆H₃₃ as the 2,3-dialkyl substituents in the butanediol-1,4 portion of the polyester. This crystallinity of polyterephthalate of 2,3-di-C₁₆H₃₃ substituted butanediol-1,4 could be assigned to side-chain crystallization of the paraffinic groups.