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Reaction of NH-pyrazoles with 1-bromoadamantane in a high pressure stainless steel autoclave (250 ml, maximum working pressure of 200 atm) gives regioselectively 1-adamantyl or 4-adamantylpyrazoles depending on the temperature.

Reaction of NH-pyrazoles with 1 -bromoadamantane in a high pressure stainless steel autoclave gives regioselectively 1-(1 -adamantyl)or 4-(1-adamantyl)pyrazoles depending on the temperature. A series of cross-experiments allows to establish the mechanism of this reaction. The molecular structure of the most simple derivative, 4-(1-adamantyl) pyrazole (3a), has been determined. Intermolecular N−H...N hydrogen bonds hold the four independent molecules together in a helix system parallel to the c axis. The crystal is built up of two centrosymmetrically related helices

The crystal and molecular structures of five 3(5)-amino-5(3)-arylpyrazoles differing in the nature of the substituent at the para position of the phenyl ring (1: X = H; 3.H2O: X = OCH3; 4: X = Cl; 5: X = Br and 6: X = NO2) have been determined by X-ray analysis. Three situations were detected in the crystal structures: the 3-tautomer is present in 1, 3 and 4; the 5-tautomer is only found in 6 and both tautomers (1:1) are observed in 5. The crystal packings are governed by NH… N O hydrogen bonds and also by OH…N interactions in the monohydrate of 3. It is worth noting that in 1, 3, 4 and 5 there are N-H…π(arene) contacts that might play a role in stabilizing the packing. Solid state 13C NMR results are consistent with the above crystallographic conclusions, thus allowing to determine that the only compound for which no good crystals have been obtained, the p-methyl derivative 2 should be a 3-amino tautomer. NMR solution studies (1H and 13C) allow to determine the 3-amino/5-amino tautomeric equilibrium constant, KT, which obeys a Hammett relationship with σp. Geometry optimizations of the 3 and 5-tautomers at semi-empirical level (AM1) were performed. In all compounds, the 3-tautomer has been found to possess a relatively lower energy by approximately 2 kcal mol−1. The potential energy surface as a function of the hybridization of the amino group and its conformation have also been analyzed.

The crystal and molecular structure of [14]paracyclo-bis-(1,2)pyrazoliumphane dibromide (1a) has been determined. The compound exists in the solid state in the chair (C) conformation while both chair (C) and boat (B) conformations are present in solution in comparable amounts. The barrier to the C ⇌ B interconversion has been determined by 1H NMR spectroscopy ( ΔG ‡ ≈ 17 kcal mol −1 ). AM1 semiempirical calculations conveniently reproduce the difference in stability between the chair (C) and the boat (B) conformations. [14]Paracyclo-bis-(1,2)pyrazolium-phane dibromide exists in the solid state in the chair conformation (X-ray crystallography) while both chair and boat conformations are present in solution in comparable amounts. The barrier to the chair boat interconversion has been determined by 1H NMR spectroscopy ( ΔG‡ ≈ 17 kcal mol −1 ).

Twenty symmetrical and asymmetrical 1,2-bisazolylethanes have been obtained from azoles and 1,2-dibromoethane or 1-chloro-2-(pyrazol-1-yl)ethane by phase transfer catalysis (PTC). The 1H and 13C nmr properties are reported and the chemical shifts of the ethylene carbon atoms discussed using an additive model.