Adamantylation of N-Unsubstituted Pyrazole Derivatives: Mechanistic and Structural Studies

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