Synthesis of poly-functionalized pyrazoles under Vilsmeier-Haack reaction conditions

Abstract

Synthesis of 1,3-disubstituted 5-chloro-1H-pyrazole-4-carbaldehydes was achieved by formylation of the corresponding 5-chloro-1H-pyrazoles under Vilsmeier-Haack conditions.

Nuclear Quadrupole Resonance Spectroscopy: Tautomerism and Structure of Functional Azoles

“…The 35 Cl NQR spectral data of a polycrystalline sample of 3,5-dichloro-l,2,4-triazole (1) differs insignificantly in the signal intensity ratios from those reported previously (Table 1) [70]. The 35 Cl NQR spectrum of 1 also differs from that expected from the single crystal X-Ray analysis (ambient temperature) [71]. These data assume that compound 1 could be a 1-H tautomer (A).…”

“…We studied the 3,5-dichloro-1,2,4-triazole (1) by 35 Cl NQR spectroscopy and showed that it also exists as the 1H-tautomer (Scheme 2) (Table 1) [46,68,69]. The 35 Cl NQR spectral data of a polycrystalline sample of 3,5-dichloro-l,2,4-triazole (1) differs insignificantly in the signal intensity ratios from those reported previously (Table 1) [70]. The 35 Cl NQR spectrum of 1 also differs from that expected from the single crystal X-Ray analysis (ambient temperature) [71].…”

“…These data assume that compound 1 could be a 1-H tautomer (A). Establishing the structure of the compounds using nuclear quadrupole spectroscopy 35 Cl and the assignment of signals in the experimental spectra without attracting quantum chemical calculations in many cases quite is difficult. In addition, 1H-form [62][63][64][65] is favorable in a solution, and the alkylation of 1,2,4-triazole affords two isomers: 1-alkyl-and 4-alkyl-1,2,4-triazole in a ratio of~10:1 [66].…”

“…We studied the 3,5-dichloro-1,2,4-triazole (1) by 35 Cl NQR spectroscopy and showed that it also exists as the 1H-tautomer (Scheme 2) (Table 1) [46,68,69].…”

“…Establishing the structure of the compounds using nuclear quadrupole spectroscopy 35 Cl and the assignment of signals in the experimental spectra without attracting quantum chemical calculations in many cases quite is difficult. The 35 Cl NQR spectral data of a polycrystalline sample of 3,5-dichloro-l,2,4-triazole (1) differs insignificantly in the signal intensity ratios from those reported previously (Table 1) [70]. The 35 Cl NQR spectrum of 1 also differs from that expected from the single crystal X-Ray analysis (ambient temperature) [71].…”