Cation radicals — intermediates in the vilsmeier-haack reaction

It was observed that cation radicals are intermediate particles in the formylation of N,N'-alkyl- or -aryldihydrophenazines with dimethyIformamide in the presence of POC1₃. The observed instantaneous cation-radical concentrations in the investigated reactions depend substantially on the concentrations and ratios of the starting reagents and may reach 50–90% based on the substrate undergoing formylation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 835–839, June, 1984.     

A synthesis of isothiazoles and pyrimidines via a vilsmeier-haack reaction

A new synthesis of isothiazoles is reported which involves the reaction of Vilsmeier salts of N,N-dimethylamides with enamino nitriles, and treatment of the intermediates successively with sodium hydrosulfide and iodine. 4-Isothiazolecarbonitriles prepared were: 3-phenyl; 3,5-dimethyl; 3,5-diphenyl; 3-methyl-5-phenyl; and 3-phenyl-5-methyl. The 5-phenylisothiazoles were obtained in low yields due to a side reaction involving the formation of pyrimidines. Pyrimidines encountered were 6-chloro-2,4-diphenyl and 6-chloro-4-methyl-2-phenylpyrimidines.     

The vilsmeier-haack reaction. IV. Reaction of phosphorus oxychloridedimethylformamide with semicarbazones

Ketone semicarbazones react with two moles of phosphorus oxychloride-dimethylformamide with the formation of 3-substituted pyrazole-4-carboxaldehydes. Aldehyde semicarbazones give, with one mole of phosphorus oxychloride-dimethylformamide, amidazines.     

The vilsmeier-haack formylation of 1,2,3-trimethylindole

The title reaction yields mainly a side-chain monosubstituted formyl derivative, namely 2-(1,3-dimethylindolyl)acetaldehyde.     

An open chain product in the reaction of benzil with thiocarbohydrazide

An open chain compound was obtained by reaction of benzil with thiocarbohy-drazide in acidic condition. Its derivative, namely, benzil bis-(5-isopropylidene-3-thiocarbohydrazone) has been structurally characterized by X-ray single crystal diffraction method. Crystallographic data: C22H26N8S2, Mr=466.62, monoclinic, space group C2/c, a=12.215(3), b=11.473(2), c=17.032 (3)A, B=98.96(2)0, V=2357.7(9)A3, Z=4, Dc=1.32 g/cm3, F(000)=1040, u(Mo Ka)=2.43 cm-1. Final R=0.050, Rw=0.061 for 1103 unique and observed reflections with I> 3o(I). The effect of the structures on the formation of the open-chain intermediates during the cyclization of (2:2) Schiff base macrocyclic compound has been discussed and a possible mechanism for the ring closure has been suggested.     

An FTIR product study of the reaction between HCO and NO2

The product distribution of the reaction (1a) $$\rm\longrightarrow OH+NO+CO$$ (1b) $$\rm\longrightarrow HNO+CO_{2}$$ (1c) $$\rm\longrightarrow H+NO+CO_{2}$$ (1d) $$\rm\longrightarrow HCO_{2}+NO$$ (1e) (1f) (1g) was investigated at room temperature in the gas phase in Ar buffer gas at 570 mbar pressure by Fourier transform infrared (FTIR) spectroscopy. Mixtures of NO₂/H₂CO/Ar were photolyzed under stationary conditions using a high‐pressure Hg lamp at λ = 300–340 nm. NO, CO, CO₂, HONO, and H₂O were found as major reaction products. A small amount of N₂O was detected at long reaction times. From the yields of CO and CO₂, branching ratios were found to be (k_1a + k_1b)/k₁ = (0.66 ± 0.10) and (k_1c + k_1d + k_1e)/k₁ = (0.34 ± 0.10). The formation of HONO was attributed to reaction ( 1a ) and/or reaction ( 1c ) followed by the reaction HNO + NO₂ → NO + HONO with a combined branching ratio of (k_1a + k_1c)/k₁ = (0.28 ± 0.10). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 136–145, 2000     

Chromatography-free product separation in the Mitsunobu reaction

Mitsunobu products can be isolated pure without column chromatography by first washing a solution of the crude reaction mixture in dichloromethane with 15% aqueous hydrogen peroxide followed by aqueous sodium sulfite. A final filtration through silica gel secures the pure Mitsunobu product.     

The Kulinkovich hydroxycyclopropanation reaction in natural product synthesis

The Kulinkovich cyclopropanation reaction provides a flexible and convenient method for the synthesis of cyclopropanols. Together with the diverse chemistry of the cyclopropanol unit, it offers access to a wide range of functionalised unsaturated and saturated compounds. The successful use in the synthesis of natural compounds is outlined in this perspective.     

An unexpected product from the reaction of imidazole with ethyl 3-ethoxy-2-nitropropenoate

Treatment of ethyl 3-ethoxy-2-nitropropenoate with imidazole afforded ethyl 1-imidazoyl(hydroximino)-acetate rather than the expected addition-elimination product.     

Structure of reaction product of phenolphthalein and epichlorohydrin

Conclusions The structure of the reaction product of phenolphthalein and epichlorohydrin in alkaline medium was established, and it was shown that it contains the lactone ring of the phthalide grouping.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 144–145, January, 1973.     

Diazoaldehyde Chemistry. Part 4vilsmeier-haack formylation of diazo compounds: A re-investigation

Diazomethyl ketones (2-diazoethanones) were reacted with the Vilsmeier reagent ((chloromethylidene)dimethylammonium chloride) to yield α-diazo-β-oxoaldehydes and chloromethyl ketones. 2′,4′-Dimethoxy-α-diazoacetophenone gave 2-chloro-1-(2,4-dimethoxyphenyl)-3-(dimethylamino)prop-2-en-1-one ( 5 ) in addition to the expected products. Phenyldiazomethanes gave the corresponding benzyl chlorides but not the (phenyl)diazoacetaldehydes even at temperatures as low as ?60°. The diazo-transfer reactions of phenylacetaldehydes and 2-azido-1-ethylpyridin-1-ium tetrafluoroborate also did not yield the expected(phenyl)diazoacetaldehydes.     

Natural product synthesis via the polybromo ketone-iron carbonyl reaction

Application of the polybromo ketone-iron carbonyl reaction to natural product synthesis is summarized. The general synthesis of tropane alkaloids has been achieved via the reductive [3+4] cyclocoupling of sym-tetrabromoacetone with N-methoxycarbonylpyrrole as the key step. Ready availability of 8-oxabicyclo[3.2.1]oct-6-en-3-one from the tetrabromoacetone and furan has opened a new, efficient entry to natural C-nucleosides including pscudouridine, pseudocytidinc, and showdomycin. The artificial analogues such as 2-thiopscudouridine, 6-azapseudouridine, pseudoisocytidine, etc., are also obtainable. The oxabicyclic ketones bearing an isopropyl substituent at the appropriate position serve as intermediates for the synthesis of naturally occurring troponoids, nezukone, α-thujaplicin, and hinokitiol (β-thujaplicin). Carbocamphenilone and camphenic acid have been prepared through the [3 + 4] reaction of 1,1,3-tribromo- 3-methylbutan-2-one and cyclopentadiene. The [3+2] cyclocondensation of an α,?a-dibromo ketone and a styrene derivative leads to the single-step synthesis of α-cuparenone. 1,3-Dibromo-3,7-dimethyloct-6-en-2- one derived from nerol (or geraniol) undergoes the biogenctic-type double cyclization. The iron carbonylassisted intramolecular [3 + 2] cyclocoupling gives camphor accompanied by other monoterpenic ketones. A mixture of campherenone and epicampherenone has been obtained from related dibromo ketone prepared from farnesols. The hetero [3+2] reaction by use of dibromo ketones and N,N-dimethylcarboxamides, forming 3 (2H)-furanones, is employable for the preparation of muscarine alkaloid derivatives.     

Relative rate and product studies of the OH-acetone reaction

The rate constants for the reaction of acetone (kH) and d6-acetone (kD) with OH radicals have been measured at atmospheric pressure over a range of temperatures by a relative rate method by using on-line mass spectrometry. The following Arrhenius expressions have been determined for these reactions (in units of cm(3) molecule(-1) s(-1)): k(H)(T) = (9.8 x 10(-13)) exp[-(484 +/- 44)/T] between 253 and 373 K, and kD(T) = (4.0 x 10(-13)) exp[-(755 +/- 89)/T] between 293 and 373 K. This is the first study to investigate the temperature dependence of kH and kD by using a relative rate method and confirms previous rate constants determined by absolute methods. Agreement of our rate constants with those determined in the absence of water suggests that the presence of water vapor has a minimal effect on the kinetics of this reaction under the conditions of our study. The observed kinetic isotope effect (kH/kD = 5.6 +/- 0.4 at 293 K) is evidence that H-atom abstraction occurs in the mechanism. The acetic acid yields of the reaction of OH with acetone and d6-acetone were also investigated by on-line mass spectrometry. Acetic acid yields show a negative temperature dependence that decreases from 0.12 at 273 K to 0.05 at 353 K. The yields of d3-acetic acid decrease from 0.20 at 283 K to 0.13 at 323 K. Kinetic modeling of our data suggests that 50-70% of the observed acetic acid in our system may be due to secondary reactions involving acetonoxy and HOx radical reactions. However, secondary chemistry cannot easily explain the observed formation of d3-acetic acid in the deuterated system, where about 90% of the observed d3-acetic acid is likely due to an OH-addition mechanism.     

Separation of uranium from complex nuclear reaction product mixtures

A solvent extraction procedure for rapid separation of uranium from complex nuclear reaction product mixtures is suggested. The procedure has been tested in batch experiments with tracer amounts of representative elements. It has also been tested with fission products and uranium tracer using the continuous chemical separation system SISAK at the Mainz TRIGA reactor.     

An inverse problem in reaction kinetics

In this paper we investigate the problem of extracting information about chemical reactions involving multiple species from the time history of the concentration of each species. The mathematical model of the kinetic system leads to a system of ordinary differential equations. Our focus is to examine whether the species’ concentrations as functions of time are sufficient to determine what chemical reactions, and at what reaction rates, have occurred. We show that within the limitation of our model, there may be many candidate reaction systems that could explain the data. Using the notion of sparsity, we provide a quantitative assessment of the question of distinguishability. We further demonstrate that sparsity enforcing approaches, such as minimizing the ℓ ₁ or the ℓ ₀ norms are not reliable. Our conclusion is that additional knowledge about the kinetic system will be necessary to reliably solve this inverse problem.