Nucleophilic substitution reactions of N-alkoxyimidoyl fluorides by carbon nucleophiles

Nucleophilic substitutions of N-alkoxybenzoimidoyl fluorides [p-ClArC(F)=NOR; R = CH3, i-Pr] by enolate-type ions have been performed to produce compounds that can exist in two tautomeric forms: the imine form{p-ClArC(Y)=NOR [Y = CH(CN)2, CH(CN)(CO2Et), CH(CO2Et)2]}or the enamine form {p-ClArC(NHOR)=C(R1)(R2) [R1, R2 = CN, CO2Et]}. These compounds display varying ratios of imine–enamine tautomerizm in chloroform: the diester compound exists almost solely in the imine form, the dicyano compound exists solely in the enamine form, and the cyano-ester compound exists in both tautomeric forms. Comparison of the imine–enamine equilibrium in chloroform of the cyano-ester compound to an analogue where the p-ClAr group has been replaced by a methyl group reveals that the aromatic ring has a significant effect on the imine–enamine distribution. The former exists in both the imine and enamine form, while the latter exists solely in the enamine form. Complete NMR characterization data for the enamine form of CH3C(NHOCH3)=C(CN)(CO2Et) is also reported. The acidity of p-ClArC(NHOR)=C(CN)2 is demonstrated by a high degree of dissociation of the enamine proton in DMSO. Substitution reactions of p-ClArC(F)=NOi-Pr by Grignard reagents (PhMgBr, CH3MgBr, and PhCCMgBr) have also been performed to produce single geometric isomers of p-ClArC(Ph)=NOi-Pr, p-ClArC(CCPh)=NOi-Pr, and p-ClArC(CH3)=NOi-Pr. A modified synthesis of N-alkoxyimidoyl fluorides, which prevents a competing reaction of the product with the solvent, is reported.Key words: N-alkoxyimidoyl fluoride, enolate ion substitution, Grignard substitution, imine–enamine tautomerizm, carbon acid.

Bisamidoximes: Synthesis and Complexation with Iron(III)

Bisamidoximes have been synthesized by the reaction of 4-methylbenzohydroximoyl chloride with 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, and 3,3′-diamino-N-methyl-dipropylamine. A monoamidoxime and a trisamidoxime were also prepared in the present work by the reaction of 4-methylbenzohydroximoyl chloride with N,N-dimethylethylenediamine and tris(2-aminoethyl)amine. Single crystal X-ray structures of three of the bisamidoximes have shown that the two amidoxime moieties have the Z configuration in all three compounds. Job’s method of continuous variations showed that three of the bisamidoximes prepared in this work form 1:1 complexes with iron(iii) and therefore are acting as tetradentate ligands.

Synthesis and Characterization of α,β-Unsaturated Hydroximoyl Chlorides and Hydroximates

New α,β-unsaturated hydroximoyl chlorides (PhC(Cl)=CHC(Cl)=NOCH3) and hydroximates (PhC(OCH3)=CHC(OCH3)=NOCH3) were prepared. The ZZ-isomer of PhC(Cl)=CHC(Cl)=NOCH3 was prepared in four steps from ethyl benzoylacetate. Ultraviolet irradiation of the ZZ-isomer gives a mixture of all four possible isomers. Sodium methoxide was reacted with these isomers to determine the configuration about the carbon–carbon double bond for each. The Z-isomers reacted with sodium methoxide to give the corresponding alkyne by elimination whereas the E-isomers gave the substitution product. The configuration about the carbon–nitrogen double bond was determined from the 1H NMR chemical shift of the NOCH3 group.

Mechanism of methoxide ion substitution in the z and e isomers of o-methylbenzohydroximoyl halides

Kinetics and stereochemical studies have been carried out on the reactions of the Z and E isomers of O-methylbenzohydroximoyl halides [1Z and 1E, ArC(X)=NOCH(3)] with sodium methoxide in 9:1 DMSO-methanol. The reactions of methoxide ion with hydroximoyl fluorides (X = F) are stereospecific. The reaction with 1Z (X = F) gives only the Z substitution product (1Z, X =OCH(3)). The reaction of methoxide ion with 1E (X = F) is less selective, giving ca. 85% E substitution product. The Hammett rho-values for the Z and E isomers (X = F) are +2.94 and +3.30, respectively. The element effects for 1Z (Ar = C(6)H(5)) are 2.21 (X = Br):1.00 (X = Cl):79.7 (X = F). The 1E element effects are (Ar = C(6)H(5)) 1.00 (X = Cl):18.3 (X = F) and (Ar = 4-CH(3)OC(6)H(4)) 1.97 (X = Br):1.00 (X = Cl):12.1 (X = F). The entropies of activation for these reactions are negative (for example, DeltaS() = -15 eu for 1Z and DeltaS() = -14 eu for 1E, Ar = 4-CH(3)OC(6)H(4), X = F). These experimental observations are consistent with a mechanism proceeding through a tetrahedral intermediate. Ab initio calculations were carried out to help explain the stereospecificity of these reactions. These calculations indicate that the tetrahedral intermediate from the Z isomer undergoes rapid elimination to the Z substitution product before stereomutation can take place. These calculations also show that the lowest barrier for rotation around the carbon-nitrogen single bond in the tetrahedral intermediate derived from 1E leads to an intermediate that eliminates fluoride ion to give E product.

Mechanisms of acid-catalyzed Z/E isomerization of imines

The kinetics and mechanism of acid-catalyzed Z/E isomerization of O-methylbenzohydroximoyl chloride (1Za and 1Ea), methyl O-methylbenzohydroximate (1Zb and 1Eb), ethyl O-methylbenzohydroximate (1Zc and 1Ec and five para and meta substituted derivatives), O-methylcinnamohydroximoyl chloride (2Za and 2Ea), and methyl O-methylcinnamohydroximate (2Zb and 2Zb) have been investigated. The kinetics of Z/E isomerization of these imines have been studied in glacial acetic acid (1Ea and 1Zc) and in dioxane solutions containing HCl, trifluoromethanesulfonic acid, or tetrafluoroboric acid (1Ea, 1Zb, 2Ea, and 2Zb). The isomerization takes place by either (a) rotation about the carbon-nitrogen double bond of the protonated imine (iminium ion rotation) or (b) nucleophilic attack on the protonated imine to form a tetrahedral intermediate that undergoes stereomutation and loss of the nucleophile (nucleophilic catalysis). The hydroximoyl chlorides 1Eaand 2Ea only isomerize by the nucleophilic catalysis mechanism. The hydroximate 1Zb appears to be capable of isomerizing by either mechanism. The hydroximate 2Zb may be isomerizing only by iminium ion rotation. Theoretical calculations support the notion that increased conjugation in the protonated imine increases the rate of iminium ion rotation.

Achieving pure electric confinement of high-charge-state plasmas

In this Brief Report, a confinement physics analysis presented previously [D. D. Dolliver and C. A. Ordonez, Phys. Rev. E 59, 7121 (1999)] is extended to consider three-dimensional electric confinement instead of one-dimensional electric and two-dimensional magnetic confinement for thermal, high-charge-state ion plasmas in nested-well solenoidal traps. Self-consistent numerical results are presented.

Confinement physics for thermal, neutral, high-charge-state plasmas in nested-well solenoidal traps

A theoretical study is presented which indicates that it is possible to confine a neutral plasma using static electric and solenoidal magnetic fields. The plasma consists of equal temperature electrons and highly stripped ions. The solenoidal magnetic field provides radial confinement, while the electric field, which produces an axial nested-well potential profile, provides axial confinement. A self-consistent, multidimensional numerical solution for the electric potential is obtained, and a fully kinetic theoretical treatment on axial transport is used to determine an axial confinement time scale. The effect on confinement of the presence of a radial electric field is explored with the use of ion trajectory calculations. A thermal, neutral, high-charge-state plasma confined in a nested-well trap opens new possibilities for fundamental studies on plasma recombination and cross-field transport processes under highly controlled conditions.

The Preparation of Imidoyl Fluorides

The first general synthesis of imidoyl fluorides is reported here. Irradiation of the initially formed Z isomers of N-methoxybenzenecarboximidoyl fluorides led to a photoequilibrium containing both the E and Z isomers. The pure E isomers were able to be isolated from these isomeric mixtures. The n.m.r. spectra of these isomers are discussed.