Methoxide ion substitution on 4-chloro-1H-2,3-benzoxazine 4 has been investigated. The rates of cyclization have been measured for (Z)- and (E)-O-(2-hydroxyethyl)benzohydroximoyl halides (PhC(X)=NOCH2CH2OH; X = Cl or Br) using potassium t-butoxide to generate alkoxide ions from the alcohols. The element effect for the Z and E isomers are kZBr/kZCl = 3.08 and kEBr/kECl = 2.38. The Z-to-E rate ratios are 0.25 (chlorides) and 0.33 (bromides). These reactions are proceeding by rate-determining nucleophilic attack by the alkoxide ion on the carbon–nitrogen double bond (AN# + DN). The restricted stereochemistry of the tetrahedral intermediates suggests that the E-hydroximoyl bromide and chloride may be undergoing unassisted ionization to form a zwitterionic intermediate that leads to product. Alternatively, the chair conformation of the tetrahedral intermediate may be undergoing a ring flip to a boat conformation in which there are antiperiplanar electron pairs that assist in the ionization of the bromide or chloride ion.

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of the imine–enamine equilibrium in chloroform of the cyano-ester compound to an analogue where the p-ClAr group has been replaced by a methyl group reveals that the aromatic ring has a significant effect on the imine–enamine distribution.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.

The first general synthesis of (Z)-O-alkylbenzohydroximidoyl iodides [ArC(I)=NOR] is reported. X-ray crystallographic structures of two of these compounds confirm that they are in the Z-configuration: p-NO2ArC(I)=NOCH3 crystallizes in space group Pnma with lattice constants a = 12.682(2) Å, b = 6.5217(15) Å, and c = 11.755(2) Å, and p-ClArC(I)=NOCH3 crystallizes in space group P21/n with lattice constants a = 15.670(4) Å, b = 5.742(4) Å, and c = 27.156(7) Å and beta angle 102.71(2). Their structures are compared to other O-alkylbenzohydroximoyl halides including p-NO2ArC(F)=NOCH3 which crystallizes in space group P21/c with lattice constants a = 3.8475(10) Å, b = 22.501(5) Å, and c = 10.088(2) Å and beta angle 91.130(11). The synthesis of two additional compounds containing the N-alkoxyimine moiety {methyl (Z)-O-methyl-4-nitrobenzothiohydroximate [p-NO2ArC(SCH3)=NOCH3] which crystallizes in space group P21/n with lattice constants a = 11.8046(15) Å, b = 7.0774(10) Å, and c = 12.2741(15) Å and beta angle 100.401(9) and (Z)-O-methyl-4-nitrobenzohydroximoyl azide [p-NO2ArC(N3)=NOCH3] which crystallizes in space group P21/c with lattice constants a = 11.753(2) Å, b = 11.310(3) Å, and c = 7.351(2) Å and beta angle 103.805(15) are also reported. Their structures are compared to (Z)-ethyl benzohydroximate [PhC(OEt)=NOH] and (Z)-O-methyl-4-nitrobenzohydroximoyl cyanide [p-NO2ArC(CN)=NOCH3] respectively. Characterizations include spectrometric identifications employing IR, 1H-NMR, 13C-NMR and mass spectrometry.

Ethyl (2Z)-3-(4-chlorophenyl)-2-cyano-3-(methoxyamino)prop-2-enoate was prepared by reacting the lithium salt of ethyl cyanoacetate with (Z)-O-methyl-4-chloroben-zohydroximoyl fluoride. This compound crystallizes in space group Pbca,with lattice constants a=7.5740(15) Å, b=11.337(2) Å, and c=30.424(5) Å at 110 K. Characterizations include spectrometric identifications employing IR, UV, and 1H and 13C NMR. The compound exists in the solid as the enamine tautomer, with the cyano group cis to the 4-chlorophenyl group (the Z configuration). The C=C and C–N bond distances are 1.3930(16) Å and 1.3278(16) Å, respectively. The N–H group forms a bifurcated hydrogen bond with acceptors C=O (intramolecular) and C≡N (intermolecular).