Investigation of m-nitroaniline formation during the Zimmermann reaction

The Zimmermann reaction for the determination of 17-ketosteroids was tested under both room-temperature and steam-distillation reaction conditions. meta-Nitroaniline was isolated from the residue of the steam distillation by ether extraction and thin-layer chromatography. Conclusive identification was by infrared spectroscopy. In contrast, m-nitroaniline was not formed under room-temperature reaction conditions, even when allowed to react for 24 hr. Similar results were also obtained for the reaction between acetone and m-dinitrobenzene under alkaline conditions. In conclusion, the results indicate that m-nitroaniline formation cannot account for the conversion of structure I to structure II under room-temperature reaction conditions as investigated herein.     

N-Tosylaziridine, a new substrate for chemical fixation of carbon dioxide via ring expansion reaction under atmospheric pressure

N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane, N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosylaziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism.     

Rheological study on the cure kinetics of two-component addition cured silicone rubber

The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature (T) on the cure kinetics was explored in detail. It was observed that the data of gel time (t _gel, i.e. the time when the reaction reaches the gel point) or a specific reaction time (t _nc) (defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected) versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour(autocatalyst) reaction model rather than Kissinger model. When the reaction time was before or equal to t _nc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than t _nc, such as to the end of reaction (t _e), the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants (k _r) under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy (E) for the two-component silicone rubber was also calculated from the results of lnt _gel, lnt _nc, and lnk _r versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent.     

Synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine derivatives via Aza-Diels–Alder reaction: evaluation of torsion effect of pyrazoylimines

A modified method for the synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine was developed through an Aza-Diels–Alder reaction of pyrazoylimines with maleimides in the sealed tube. Based on the control experiment, the yields for the Aza-Diels–Alder reaction seemed proportional to the suitable torsion conformation of pyrazoylimine, which was modulated by N,N-disubstituted amidinyl moiety. The versatile sealed tube technique was also proved to promote the higher isolated yields in the Aza-Diels–Alder reaction.     

Isothermal cure kinetics of uncatalyzed and catalyzed diglycidyl ether of bisphenol-A/carboxylated polyester hybrid powder coating

The thermal cure behavior of diglycidyl ether bisphenol-A/carboxylated polyester hybrid powder coating system in the absence and presence of catalyst was monitored using differential scanning calorimetry. Curing temperatures were between 160 and 200?°C. The experimental results showed an autocatalytic behavior of the reaction, which could be described by the model proposed by Kamal. This model includes two rate constants k ₁ and k ₂ and two reaction orders m and n. The activation energies E _a1 and E _a2 of these rate constants were 51.7 and 42.3?kJ/mol for uncatalyzed cure reaction and 40.6 and 35.0?kJ/mol for externally catalyzed reaction. The average order of the overall reaction was found to be 2.45 and 2.72 for uncatalyzed and catalyzed system, respectively. Except for the late stage of cure reaction, the model agreed well with the experimental data, especially at high temperatures and in externally catalyzed cure reaction. A diffusion factor was introduced into the model to account for the effect of diffusion on the cure rate. The modified model greatly improved the predicated data at the late stage of cure reaction.     

Microwave-accelerated cross-metathesis reactions of N-allyl amino acid substrates

Microwave heating has been utilised for the cross-metathesis reaction of N-allyl amino acid substrates to generate olefin homodimers. Remarkable acceleration of the cross-metathesis reaction (minutes compared to hours) over conventional reflux heating was observed. In addition, improved reaction yields and similar E/Z ratios for the cross-metathesis products were achieved.     

A novel enzymatic tandem process: utilization of biocatalytic promiscuity for high stereoselective synthesis of 5-hydroxyimino-4,5-dihydrofurans

A lipase-catalyzed protocol for the synthesis of 5-hydroxyimino-4,5-dihydrofurans via tandem coupling between β-nitrostyrenes and 1,3-dicarbonyl compounds was developed in a ‘one-pot’ strategy. A series of β-nitrostyrenes were employed to expand the scope of this new biocatalytic promiscuity with high stereoselectivity (Z/E up to 99:1) and moderate to good yields. The reaction activity of 1,3-cyclohexanedione was found to be better than linear 2,4-pentanedione, while ethyl acetoacetate and diethylmalonate were not suitable for this reaction under the same conditions. Single-crystal X-ray diffraction analysis indicated that the reaction was stereoselective and Z-stereomer was found to be the major product. A reaction mechanism was supposed to elucidate the biocatalytic process.     

A new synthesis of cyanocyclopropanes by the intramolecular alkylation of magnesium carbenoids as the key reaction

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, derived from ketones and chloromethyl p-tolyl sulfoxide, with cyanomethyllithium gave adducts in quantitative yields. Treatment of the adducts with i-PrMgCl in THF resulted in the formation of cyanocyclopropanes via the intramolecular alkylation of the generated magnesium carbenoids. The intermediate of this reaction was proved to be a cyclopropylmagnesium chloride, and it was found to be reactive with electrophiles to give multi-substituted cyanocyclopropanes. The key reaction, intramolecular alkylation of magnesium carbenoid, is the first example for the reaction of the magnesium carbenoids with nitrile-stabilized carbanions.     

Kinetic parameters of radical reactions of 2-mercaptobenzothiazole with quinone imines

The chain reaction of N,N′-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole was studied by two methods developed earlier for the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole. In the methods used, the kinetic scheme of the reaction is simplified by creating conditions under which the rates of all stages except radical generation and decay can be neglected. One of the methods was updated. For the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole, both methods gave close results; for the chain reaction of N,N′-diphenyl-1,4-phenylenediamine with 2-mercaptobenzothiazole, the results differed by approximately one order of magnitude.     

[3+2] Cycloaddition of metal-containing azomethine ylides for highly efficient synthesis of mitosene skeleton

Efficient synthesis of tricyclic indole derivatives bearing a substituent at the 3-position of the indole nucleus was achieved by the [3+2] cycloaddition reaction of transition metal-containing azomethine ylides derived from N-(o-alkynylphenyl)imines with vinyl ethers. Third-row transition metal complexes, especially PtCl₂, turned out to be highly efficient for the reaction of internal alkynes and imidate substrates with wide generality. Moreover, as strong support for the reaction mechanism, the intermediate Pt-carbene complex was found to undergo intramolecular C-H bond insertion reaction to give tetracyclic indoline derivatives when benzyl vinyl ether was employed as a dipolarophile. This protocol provided a facile synthesis of highly functionalized tricyclic indole derivatives found as the basic skeleton of the mitosene family, such as mitomycin C.     

Random cross-linked poly(styrene-co-maleic anhydride): Characterization of cross-linking intermediates by size exclusion chromatography

The cross-linking reaction of poly(styrene-co-maleic anhydride) (SMA) with ethylene glycol (EG) was monitored using size exclusion chromatography. On-line viscosity and static light scattering detection provided [η] and R_g for structural analysis of the cross-linking intermediates. With increasing reaction time a decrease of the expansion exponent α of the Kuhn-Mark-Houwink-Sakurada relationship was observed. A change from coiled structures to spherical molecules during the cross-linking reaction was confirmed by analyzing the fractal dimensions of the molecules after different reaction times. The calculation of the branching parameters g and g′ revealed the formation of contracted branched molecules. The connection of SMA chains by EG leads to a contraction of the polymers with increasing molecular weight.     

Electrochemically mediated decarboxylative acylation of N-nitrosoanilines with α-oxocarboxylic acids

An efficient palladium-catalyzed electrooxidation C–H acylation reaction of N-nitrosoanilines with α-oxocarboxylic acids was developed. The anodic oxidation of the Pd(Ⅱ) intermediate was found to be the key to complete the reaction. In this case, the N-nitroso group was observed to be an effective directing group for C–H activation reaction. Moreover, the synthetic transformation of derivatives of natural products(L-menthol, dehydroepiandrosterone, and pregnenolone) was successfully realized. Fi...     

Synthesis of oxindoles via Cu-mediated reactions between N-phenylacrylamides and ethyl 2-bromo-2-methylpropionate

A novel way of synthesizing alkylated oxindoles via Cu-mediated atom transfer radical addition reaction between N-phenylacrylamides and ethyl 2-bromo-2-methylpropionate has been described. It was found that the use of N,N,N′,N′-1,1,2,2,-tetramethylethylenediamine as ligand was important for achieving good yields. Additionally, the use of DMSO as solvent and running the reaction at 130?°C were also crucial. In some cases, the product can be further brominated when the reaction temperature was raised to 150?°C.     

Carbon radical addition to N-sulfonylimines mediated by triethylborane or zinc

The utility of N-sulfonylimines as radical acceptors was investigated under the different reaction conditions such as the stannyl radical-mediated addition reaction, the triethylborane-mediated tin-free radical reaction, and the zinc-mediated aqueous-medium radical reaction. The alkyl radical addition reaction of N-sulfonylimines proceeded effectively without the activation by Lewis acid. These reactions were successfully extended to one-pot reactions for preparing a wide range of amine derivatives.     

Isocyanide based multicomponent reactions of oxazolidines and related systems

N-Alkyloxazolidines react in a multicomponent reaction with carboxylic acids and isocyanides to give N-acyloxyethylamino acid amides. The previously reported reaction conditions were improved using a design of experiments approach (DoE). Under the optimised conditions, good yields of the N-acyloxyethylamino acid amide products are obtained both via a three- or four-component approach from N-alkylethanolamines, aldehydes/ketones, isocyanides and carboxylic acids. The reaction of oxazolidines without a nitrogen substituent was found to give either the expected Ugi products or the N-acyloxyethylamino acid amides depending on the choice of reaction conditions. Optimised reaction conditions were also developed for the ring-expansion of oxazolidines to morpholin-2-ones via reaction with an isocyanide followed by hydrolysis. The mechanistic pathway of the multicomponent reaction was briefly investigated using an ¹⁸O labelling experiment. The carboxylic acid component can be replaced by a range of other acidic nucleophiles including thiobenzoic acid, thiophenol or 5-phenyltetrazole, which are incorporated via an alternative pathway. These latter reactions can also be applied to 2-aminotetrahydrofurans, 2-aminotetrahydropyrans or 4-hydroxybut-2-one, further extending the structural diversity of the multicomponent reaction products.     

Reactions of O with CO van der Waals molecules and clusters

The reaction of O(³ P) with COR _m clusters to produce electronically excited CO₂ was studied under molecular beam conditions. It was found that the spectrum of the chemiluminescence produced extended from the blue all the way to the near infrared. The dependence of the total emission intensity on stagnation pressure was investigated for (CO) _m as well as for COR _m , R=He, Ne, Ar, N₂, CO₂ and SO₂. The low pressure data indicate that small (CO) _m polymers are more efficient than clusters of CO with other species in inducing the chemiluminescent reaction. The larger CO-rare gas clusters, however, exhibited larger reaction cross-sections than those of the CO polymers. Rare gas clusters ofm≧5, on the other hand have successively smaller cross sections for reaction. The reactivity of the CO₂ and SO₂ clusters seems to peak at aboutm=1 and then decreases for larger species. An equilibrium model for cluster formation was proposed and it was found capable of explaining and simulating the experimental observations. Contrary to what was reported from afterglow experiments, no barrier for the reaction was detected.     

A visible-light-promoted cross-dehydrogenative-coupling reaction of N-arylglycine esters with imidazo[1,2-a]pyridines

A mild and convenient visible-light-promoted cross-dehydrogenative-coupling reaction between N-arylglycine esters and imidazo[1,2-a]pyridines for the construction of CC bond was developed. A range of N-arylglycine esters and imidazo[1,2-a]pyridines were able to undergo the CDC reaction readily to afford α-heteroaryl substituted α-amino acid derivatives in good to excellent yields. A tentative mechanism for the photoredox reaction was also proposed. Importantly, the use of copper(II) salt as the sole catalyst in this visible-light-promoted transformation makes this reaction sustainable and practical.     

Regioselective synthesis of β-fluoro-α,β-unsaturated ketones by the reaction of β-diketones with DFMBA

The deoxyfluorination reaction of β-diketones with N,N-diethyl-α,α-difluoro-m-methylbenzylamine (DFMBA) gave β-fluoro-α,β-unsaturated ketones in good yields. The reaction proceeded regioselectively, and only one regioisomer was obtained from the unsymmetrical 1-aryl-1,3-diketones. The reaction is applicable to diketones with a trifluoromethyl group, obtaining good yields of 3,4,4,4-tetrafluorobutenones. We used the resulting β-fluoro-α,β-unsaturated ketones for the reaction with lithium dialkyl cuprates.     

New synthesis of multisubstituted cyanocyclopropanes by the intramolecular SN2 alkylation and 1,3-CC insertion reaction of magnesium carbenoids as the key reactions

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides derived from ketones and aldehydes with lithium α-cyano carbanions gave nitrile adducts in high to quantitative yields. Treatment of the nitrile adducts derived from acetonitrile with excess i-PrMgCl in THF resulted in the formation of cyanocyclopropanes via the intramolecular S_N2 alkylation of the generated magnesium carbenoids. The intermediate of this reaction was proved to be a cyclopropylmagnesium chloride and was reactive with electrophiles to give multisubstituted cyanocyclopropanes. On the other hand, the reaction of the nitrile adducts derived from arylacetonitriles with i-PrMgCl resulted in the formation of 2-arylcyanocyclopropanes by the 1,3-carbon–carbon (1,3-CC) insertion reaction of the generated magnesium carbenoid intermediates. This reaction was found to proceed in a highly stereospecific manner. The key reactions, intramolecular S_N2 alkylation and 1,3-CC insertion reaction of the magnesium carbenoids, are the first examples for the reaction of the magnesium carbenoids bearing a nitrile functional group.     

Synthesis of new eburnamine-type alkaloid via direct hydroalkoxylation

This study concerns the preparation of a new eburnamine-type alkaloid, methyl (3α,14β,15β,16α)-17,18-didehydro-14,15-dihydroeburnamine-15-methoxy-14-carboxylate (VIII). This alkaloid was prepared from (+)-17,18-dehydroapovincamine (V) using Lewis acid and/or ion exchange resin as catalyst. The hydroalkoxylation reaction of V with methanol was investigated in terms of catalyst, solvent, temperature, and time of reaction. A one-pot method for synthetising this alkaloid was established. The optimal conditions for the reaction are discussed.