Nickel-catalyzed cycloaddition of alkynes and isocyanates

A mild and general route for preparing 2-pyridones from isocyanates and diynes is described. Ni imidazolyidene complexes were used to mediate cyclizations between both internal and terminal diynes with aryl and alkyl isocyanates. In addition, the efficacy of this protocol allows for the preparation of a fused seven-membered pyridone and for three component cyclizations.     

Polyaryl anion radicals via alkali metal reduction of arylurea oligomers

A series of N-methylated polyarylurea oligomers have been reduced with potassium metal in HMPA. These reductions result in the transient formation of arylurea anion radicals, which undergo reductive elimination of the urea linkages. The aryl moieties appear in the products as the anion radicals of oligoaryl systems. The reaction is intramolecular, and the sequencing in the polyaryl anion radical remains the same as in the polyarylureas due to the urea-enforced pi-pi stacking interactions.     

H2O2环氧化TAIC制备TGIC

三烯丙基异氰尿酸酯（TAIC）;异氰尿酸三缩水甘油酯（TGIC）;碳酸氢铵;H2O2;反应机理     

4-thioxo-2-azetidinones by cycloaddition of thioketenes with isocyanates

The (2+2) cycloaddition of thioketenes $\text{1}$ with isocyanates $\text{2}$ yields 4-thioxo-2-azetidinones $\text{3}$, which can be hydrolyzed to the N-unsubstituted compound $\text{4}$ and thus used as versatile intermediates.     

Solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates

The first solid-phase synthesis of oxazolidinones by cycloaddition of resin-bound epoxides with isocyanates is described. Synthesis of the title compounds was achieved by alkylation of resin-bound carbamates with glycidyl tosylate, followed by cycloaddition of the resulting epoxides with isocyanates at elevated temperature in high yields and purity. Because N-aryloxazolidinones have been known to possess various biological activities, this method is useful from the viewpoint of drug discovery.     

Nitropyridyl isocyanates in 1,3‐dipolar cycloaddition reactions

The reactivity of 3‐nitro‐4‐pyridyl isocyanate ( 7 ) and 5‐nitropyridin‐2‐yl isocyanate ( 9 ) in 1,3‐dipolar cycloaddition reactions with azides and pyridine N‐oxides has been investigated. 1,3‐Dipolar cycloaddition to trimethylsilylazide (TMSA) afforded the respective tetrazolinones, 1‐(3‐nitropyridin‐4‐yl)‐1H‐tetrazol‐5(4H)one ( 8 , 50 %) and 1‐(5‐nitropyridin‐2‐yl)‐1H‐tetrazol‐5(4H)one ( 11 , 64 %). Respectively, 1,3‐dipolar cycloaddition of nitropyridyl isocyanates 7 and 9 to 3,5‐dimethylpyridine N‐oxide ( 14 ), 3‐methylpyridine N‐oxide ( 21 ) and pyridine N‐oxide ( 22 ) gave the substituted amines, 3,5‐dimethyl‐N‐(3‐nitropyridin‐4‐yl)pyridin‐2‐amine ( 17 ), 3,5‐dimethyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 20 ), N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 24 ), 5‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 23 ) and 3‐methyl‐N‐(5‐nitropyridin‐2‐yl)pyridin‐2‐amine ( 25 ) in 65 ‐ 80 % yield, obtained by cycloaddition, rearrangement and decarboxylation. The results demonstrate that the nitropyridyl isocyanates ( 7,9 ) readily undergo 1,3‐dipolar cyloaddition reactions similar to phenyl isocyanates.     

4 + 1] cycloaddition of N-heterocyclic carbenes with vinyl isocyanates

[reaction: see text] N-Heterocyclic carbenes have been found to undergo [4 + 1] cycloaddition with various vinyl isocyanates to afford functionalized hydroindolone products.     

Infrared spectra of tetracyanothiophene anion radicals

Infrared spectra of anion radicals of tetracyanothiophene were recorded at −78°C. Large difference of the spectra was observed between the neutral molecule and the anion radicals and was interpreted by the change in the electronic structure.     

EPR spectra of halogenonitromethane anion radicals

Conclusions It was deduced that fluorine is in a -combined state in the anion radicals we studied; this was based on an analysis of the EPR spectra of a series of fluoronitroalkane anion radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 458–460, February, 1969.In conclusion, the authors express their appreciation to A. A. Fainzil'berg for his interest in our work.     

Investigation of organosilicon radicals : I. Methylphenylsilane anion radicals

CNDO/2 calculations with an spd basis set have been carried out on methyl-phenylsilane anion radicals, and the calculated spin density values compared with the experimental hyperfine coupling constants. The CNDO method overestimates the role of d orbitals and the partial charges on hydrogen atoms attached to silicon atom. The partial charge distribution and the carbonsilicon bond order in the anion radicals and the corresponding neutral molecules are discussed. The equilibrium carbonsilicon bond distance in the trimethylphenylsilane molecule and corresponding anion radical have also been investigated.     

Reduction of isocyanates and carbodiimides via hydrosilylation

The hydrosilylation of isocyanates is promoted by palladium catalysts and affords N-silylformamides or C-silylamides. The orientation of the reaction depended upon the structure of isocyanates. The reaction of carbodiimides with silicon hydrides, catalyzed by PdCl₂ or (Ph₃P)₃RhCl, required higher temperatures to give N-silylformamidines. The adducts obtained in these reactions are precursors to formamides, formamidines, and their N-acetyl derivatives.     

Photoinduced orientational order of dichloride anion radicals

The photo-orientation of dichloride anion radicals (Cl₂^−·) in a glassy solution of 5 M LiCl is discussed. The quantitative characteristics of orientation of paramagnetic molecules were determined using the anisotropy of optical absorption and the angular dependence of the EPR spectrum. The orientational distribution function of ordered anion radicals was determined by joint computer modeling of the EPR spectrum recorded at different directions of the symmetry axis of a sample relative to the magnetic field of a spectrometer. It was found that the value of the order parameter (−0.1 ± 0.01), calculated from the orientational distribution function coincides with the value obtained under the measurements of the linear dichroism in the range of the detection error (−0.12 ± 0.01).     

Electroconductive polypyrrole doped with tetracyanoethylene anion radicals

An electroconductive polymer doped with tetracyanoethylene anion radicals was obtained by chemical oxidation of undoped polypyrrole. Its electronic absorption spectra were investigated. Broadening of the line of the EPR spectrum was observed when the anion radical was introduced into the polymer; this may be due to slow spin-spin exchange between the radical and the polar chain of the polymer.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 3, pp. 260–263, May–June, 1993.This research was financed by the State Committee of Ukraine for Problems in Science and Technology from fundamental-research.     

ESR spectra of anion radicals of phenazine derivatives

The ESR spectra are reported for electrolytically generated radicals. The hyperfine structure is found to be due to primary interaction of the unpaired electron with two nitrogen atoms, the quintet being then split by the ring protons. A quantum calculation of the spin density agrees satisfactorily with the results.     

Asymmetric polymerization via cycloaddition reactions

The reaction of N‐phthaloyl‐L ‐leucine acid chloride (1) with isoeugenol (2) was carried out in chloroform, and novel optically active isoeugenol ester derivative 3 as a chiral monomer was obtained in high yield. Compound 3 was characterized by ¹H‐NMR, IR, and mass and elemental analysis and then was used for the preparation of model compound 5 and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione, PhTD (4), was allowed to react with compound 3. The reaction is very fast and gives only one diastereomer of 5 via Diels–Alder and ene pathways in quantitative yield. In order to explain this diastereoselectivity, a nonconcerted two‐step mechanism involving benzylic cation (BC) and aziridinium (AI) have been proposed for the Diels–Alder and ene reactions, respectively. The polymerization reactions of novel monomer 3 with bis(triazolinedione)s [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane (8) and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane] (9)] were performed in N,N‐dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel optically active polymers 10 and 11 via repetitive Diels–Alder–ene polyaddition reactions. These polymers have inherent viscosities in a range about 0.18–0.22 dL/g. Some physical properties and structural characterizations of these new polymers have been studied and are reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1211–1219, 1999     

Non-aqueous capillary electrophoresis of p-quinone anion radicals.

The electrophoretic detection of two kinds of p-quinone anion radicals arising from the electrolysis of benzoquinone and chloranil was achieved by employing an acetonitrile medium. Sufficient dehydration of a running solution was necessary for the detection of the benzoquinone anion radical. Oxygen in the running solution also caused a serious decrease in the amount of the benzoquinone anion radical during electrophoresis. The addition of methanol as a hydrogen-donor decreased the electrophoretic mobility of the benzoquinone anion radical significantly, while that of the chloranil anion radical was little changed. This result is interpreted in terms of hydrogen-bonding interaction between the p-quinone anion radicals and methanol, reflecting the magnitude of their proton-accepting ability (benzoquinone anion radical > chloranil anion radical).     

A nickel(0) catalyzed cycloaddition of alkynes and isocyanates that affords pyrimidine-diones

A Ni/N-heterocyclic carbene catalyzed cycloaddition of one alkyne and two isocyanates that affords pyrimidine-dione is described. The key to the success of this protocol is the use of unsymmetrically substituted alkynes that favors the formation of pyrimidine-diones over pyridones. A variety of pyrimidine-diones were prepared. A one-pot cycloaddition and Stille coupling were reported for tributyl(1-propynyl)tin. Competition studies also provide insights into the mechanism of the cycloaddition.     

Rhodium-catalyzed [2 + 2 + 2] cycloaddition of alkenyl isocyanates and alkynes

A rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition between alkenyl isocyanates and alkynes has been developed. Heating a mixture of an alkenyl isocyanate and a symmetrical internal alkyne in the presence of [Rh(ethylene)2Cl]2/P(4-OMe-C6H4)3 in toluene delivers substituted indolizinones and quinolizinones. Depending on the substrates, a rare fragmentation of the isocyanate unit can be involved within the cycloaddition process to furnish a vinylogous amide embedded in the indolizinone.