Stability Studies of N-Acylimidazoles

Elucidation of the E-Amide Preference of N-Acyl Azoles

“…Spectral data for compounds 1 , , 2 , , 3 , 4 , 5a , 5c , 6a , and 7a are consistent with values previously reported in the literature.…”

“…Since then, N -acyl azoles have been considered to be mild acylating agents as alternatives to acyl halides and anhydrides . Recently, it has been revealed that the sterically hindered N -acylimidazoles show better stability toward nucleophiles than unhindered ones, and several stability studies of various N -acylimidazoles have been published . In the course of our stereochemical and physicochemical analyses of biologically active molecules, we also found that the 2′,6′-disubstituted N -benzoyl imidazoles were unexpectedly stable .…”

“…Based on VT NMR, the activation free energy barrier to rotation of the N–C axis of E / Z -amide conformers of 5b was estimated (coalescence method: Δ G c ⧧ = 11.8 kcal/mol; line shape analysis: Δ G ⧧ (at −50 °C) = 12.1 kcal/mol). Similarly, the two sets of resonances at −90 °C ( E / Z = 2.8:1) were observed in N -2′,4′,6′-trimethylbenzoyl imidazole 5c , and the activation free energy barrier to rotation of the E / Z -amide conformers was estimated by VT NMR (coalescence method: Δ G c ⧧ = 13.3 kcal/mol; line shape analysis: Δ G ⧧ (at −20 °C) = 13.3 kcal/mol).…”

“…For N -benzoyl imidazole 5a , only one set of resonances was observed in the VT NMR spectrum irrespective of temperature (−90 °C–100 °C) . In contrast, N -2′,4′,6′-trichlorobenzoyl imidazole 5b provided two sets of resonances at −90 °C, which are similar to those of the E / Z -amide conformers of N -acetyl imidazole 1 .…”

Elucidation of the E-Amide Preference of N-Acyl Azoles

“…Spectral data for compounds 1 , , 2 , , 3 , 4 , 5a , 5c , 6a , and 7a are consistent with values previously reported in the literature.…”

“…Since then, N -acyl azoles have been considered to be mild acylating agents as alternatives to acyl halides and anhydrides . Recently, it has been revealed that the sterically hindered N -acylimidazoles show better stability toward nucleophiles than unhindered ones, and several stability studies of various N -acylimidazoles have been published . In the course of our stereochemical and physicochemical analyses of biologically active molecules, we also found that the 2′,6′-disubstituted N -benzoyl imidazoles were unexpectedly stable .…”

“…Based on VT NMR, the activation free energy barrier to rotation of the N–C axis of E / Z -amide conformers of 5b was estimated (coalescence method: Δ G c ⧧ = 11.8 kcal/mol; line shape analysis: Δ G ⧧ (at −50 °C) = 12.1 kcal/mol). Similarly, the two sets of resonances at −90 °C ( E / Z = 2.8:1) were observed in N -2′,4′,6′-trimethylbenzoyl imidazole 5c , and the activation free energy barrier to rotation of the E / Z -amide conformers was estimated by VT NMR (coalescence method: Δ G c ⧧ = 13.3 kcal/mol; line shape analysis: Δ G ⧧ (at −20 °C) = 13.3 kcal/mol).…”

“…For N -benzoyl imidazole 5a , only one set of resonances was observed in the VT NMR spectrum irrespective of temperature (−90 °C–100 °C) . In contrast, N -2′,4′,6′-trichlorobenzoyl imidazole 5b provided two sets of resonances at −90 °C, which are similar to those of the E / Z -amide conformers of N -acetyl imidazole 1 .…”

Synthesis, Characterization, and in Vitro Evaluation of Novel Ruthenium(II) η6-Arene Imidazole Complexes

“…The desired compounds precipitated directly from the reaction mixture and were isolated by filtration. For the more labile ligand N- benzoylimidazole (benzoylimid), which was synthesized by a literature protocol, the conversion was carried out in CH 2 Cl 2 at room temperature.

3 Structures of 8a − c and 11 − 13 .

…”

Elucidation of the E-Amide Preference of N-Acyl Azoles

“…Spectral data for compounds 1 , , 2 , , 3 , 4 , 5a , 5c , 6a , and 7a are consistent with values previously reported in the literature.…”

“…Since then, N -acyl azoles have been considered to be mild acylating agents as alternatives to acyl halides and anhydrides . Recently, it has been revealed that the sterically hindered N -acylimidazoles show better stability toward nucleophiles than unhindered ones, and several stability studies of various N -acylimidazoles have been published . In the course of our stereochemical and physicochemical analyses of biologically active molecules, we also found that the 2′,6′-disubstituted N -benzoyl imidazoles were unexpectedly stable .…”

“…Based on VT NMR, the activation free energy barrier to rotation of the N–C axis of E / Z -amide conformers of 5b was estimated (coalescence method: Δ G c ⧧ = 11.8 kcal/mol; line shape analysis: Δ G ⧧ (at −50 °C) = 12.1 kcal/mol). Similarly, the two sets of resonances at −90 °C ( E / Z = 2.8:1) were observed in N -2′,4′,6′-trimethylbenzoyl imidazole 5c , and the activation free energy barrier to rotation of the E / Z -amide conformers was estimated by VT NMR (coalescence method: Δ G c ⧧ = 13.3 kcal/mol; line shape analysis: Δ G ⧧ (at −20 °C) = 13.3 kcal/mol).…”

“…For N -benzoyl imidazole 5a , only one set of resonances was observed in the VT NMR spectrum irrespective of temperature (−90 °C–100 °C) . In contrast, N -2′,4′,6′-trichlorobenzoyl imidazole 5b provided two sets of resonances at −90 °C, which are similar to those of the E / Z -amide conformers of N -acetyl imidazole 1 .…”

Synthesis, Characterization, and in Vitro Evaluation of Novel Ruthenium(II) η6-Arene Imidazole Complexes

“…The desired compounds precipitated directly from the reaction mixture and were isolated by filtration. For the more labile ligand N- benzoylimidazole (benzoylimid), which was synthesized by a literature protocol, the conversion was carried out in CH 2 Cl 2 at room temperature.

3 Structures of 8a − c and 11 − 13 .

…”

Elucidation of the E-Amide Preference of N-Acyl Azoles

“…Spectral data for compounds 1 , , 2 , , 3 , 4 , 5a , 5c , 6a , and 7a are consistent with values previously reported in the literature.…”

“…Since then, N -acyl azoles have been considered to be mild acylating agents as alternatives to acyl halides and anhydrides . Recently, it has been revealed that the sterically hindered N -acylimidazoles show better stability toward nucleophiles than unhindered ones, and several stability studies of various N -acylimidazoles have been published . In the course of our stereochemical and physicochemical analyses of biologically active molecules, we also found that the 2′,6′-disubstituted N -benzoyl imidazoles were unexpectedly stable .…”

“…Based on VT NMR, the activation free energy barrier to rotation of the N–C axis of E / Z -amide conformers of 5b was estimated (coalescence method: Δ G c ⧧ = 11.8 kcal/mol; line shape analysis: Δ G ⧧ (at −50 °C) = 12.1 kcal/mol). Similarly, the two sets of resonances at −90 °C ( E / Z = 2.8:1) were observed in N -2′,4′,6′-trimethylbenzoyl imidazole 5c , and the activation free energy barrier to rotation of the E / Z -amide conformers was estimated by VT NMR (coalescence method: Δ G c ⧧ = 13.3 kcal/mol; line shape analysis: Δ G ⧧ (at −20 °C) = 13.3 kcal/mol).…”

“…For N -benzoyl imidazole 5a , only one set of resonances was observed in the VT NMR spectrum irrespective of temperature (−90 °C–100 °C) . In contrast, N -2′,4′,6′-trichlorobenzoyl imidazole 5b provided two sets of resonances at −90 °C, which are similar to those of the E / Z -amide conformers of N -acetyl imidazole 1 .…”

Synthesis, Characterization, and in Vitro Evaluation of Novel Ruthenium(II) η6-Arene Imidazole Complexes

“…The desired compounds precipitated directly from the reaction mixture and were isolated by filtration. For the more labile ligand N- benzoylimidazole (benzoylimid), which was synthesized by a literature protocol, the conversion was carried out in CH 2 Cl 2 at room temperature.

3 Structures of 8a − c and 11 − 13 .

…”