3-Halomethylated cyclic nitronates: synthesis and nucleophilic substitution

A method for the introduction of a halogen atom into the methyl group attached to the C-3 atom of five- and six-membered cyclic nitronates (isoxazoline N-oxides and oxazine N-oxides, respectively) has been studied. The process involves silylation of starting 3-methyl-substituted cyclic nitronates followed by halogenation of the resulting N-(silyloxy)enamines. While five- and six-membered cyclic enamines behave similarly toward elemental bromine and iodine, their reactions with NBS give different products, that were rationalized by stereoelectronic effects. The obtained halogenated nitronates were coupled with various nucleophiles affording new nitronates functionalized at the C-3 position.     

Nucleophilic trifluoromethylation with organoboron reagents

Potassium trialkoxy(trifluoromethyl)borates are shown to behave as convenient reagents for nucleophilic trifluoromethylation of non-enolizable aldehydes and N-tosylimines to give CF₃-substituted alcohols and N-tosylamines in good yields.     

Oxodiazonium ion generation 5. 3-(N-Nitroamino)-4-phenylfuroxan: synthesis and reactivity

3-(N-Nitroamino)-4-phenylfuroxan, the first representative of the furoxan series that contains the N-nitroamino group in position 3 of the furoxan ring, was obtained. This compound is not very stable; its structure was confirmed by chemical transformations into an ammonium salt and N- and O-methyl derivatives. Under standard conditions for oxodiazonium ion generation from nitramine, 3-(N-nitroamino)-4-phenylfuroxan underwent a transformation into the corresponding azofuroxan, viz., 3,3??-diazenediylbis(4-phenyl-1,2,5-oxadiazole 2-oxide), while the O-methyl derivative of 3-(N-nitroamino)-4-phenylfuroxan yielded 2-hydroxyimino-2-phenylacetonitrile. The changed reactivity of the oxodiazonium ion was explained by its intramolecular interaction with the exocyclic O atom of the furoxan system.     

Synthesis and nitration of 3-R-4-(2,2,2-trinitroethyl)aminofuroxans

Simple methods for the synthesis of 3-R-4-(2,2,2-trinitroethyl)aminofuroxans were developed based on the Mannich reaction of N,N′-bis(3-R-furoxan-4-yl)methylenediamines with trinitromethane or 3-R-4-aminofuroxans with trinitroethanol or with CH₂O and trinitromethane. The Mannich bases obtained were studied in the nitration reaction, which showed their ability to form nitramines depending on substituents on the furoxan ring.     

Synthesis of PDE IVb Inhibitors. 3. Synthesis of (+)-, (-)-, and (±)-7-[3-(cyclopentyloxy)-4-methoxyphenyl]hexahydro-3H-pyrrolizin-3-one via reductive domino transformations of 3-β-carbomethoxyethyl-substituted six-membered cyclic nitronates

Simple three-step asymmetric and racemic syntheses of GlaxoSmithKline's highly potent PDE IVb inhibitor 1 were developed. The suggested approach is based on reductive domino transformations of 3-β-carbomethoxyethyl-substituted six-membered cyclic nitronates, which are easily accessed by a stereoselective [4 + 2] cycloaddition of an appropriate nitroalkene to vinyl ethers. In vitro studies of PDE IVb inhibition by enantiomeric pyrrolizidinones (+)-1 and (-)-1 were performed.     

Nucleophilic trifluoromethylation of arylidene Meldrum’s acids

A method for the trifluoromethylation of arylidene Meldrum’s acids using Me₃SiCF₃ followed by transformation of the initial products to CF₃-substituted esters and alcohols is described. The sequence of reactions is performed without isolation of intermediate compounds furnishing the final products in good overall yields.     

Stochastic langevin model for flow and transport in porous media

We present a new model for fluid flow and solute transport in porous media, which employs smoothed particle hydrodynamics to solve a Langevin equation for flow and dispersion in porous media. This allows for effective separation of the advective and diffusive mixing mechanisms, which is absent in the classical dispersion theory that lumps both types of mixing into dispersion coefficient. The classical dispersion theory overestimates both mixing-induced effective reaction rates and the effective fractal dimension of the mixing fronts associated with miscible fluid Rayleigh-Taylor instabilities. We demonstrate that the stochastic (Langevin equation) model overcomes these deficiencies.     

Dineutron configurations in neutron-excess nuclei from the viewpoint of the diffraction model

Cross sections measured for the interactions of incident neutron-excess nuclei ⁶He and ¹¹Li with other nuclei are analyzed in terms of expressions obtained for relevant integrated cross sections within the diffraction approximation. The results of this analysis suggest that there exists a dineutron configuration in the ⁶He nucleus and that there is no such configuration in the ¹¹Li nucleus. On the basis of calculations performed for various observables, some new specific experiments are proposed for discovering dineutrons more reliably in nuclei having a neutron halo.     

Electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom

The electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom was observed for the first time when 6-bromo-2,4-bis(tert-butyl-NNO-azoxy)-5-chloro-1,3-phenylenediamine was treated with bromine in AcOH. The structural factors promoting this reaction are discussed. The direction of the replacement was confirmed by PM3 calculations of the heats of formation of intermediate cationic σ-adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2131–2134, November, 1999.