Synthesis and analytical resolution of chiral pyrazoles derived from (5R)-dihydrocarvone

Abstract

In the course of the development of chiral hydrotris(pyrazolyl)borate ligands for unidirectional molecular machines, we have investigated the preparation of original chiral pyrazoles using (5R)-dihydrocarvone as starting material. Of the two synthetic routes examined and described in this article, the most efficient one involved the formation of the pyrazole ring in a last step. This method appeared very efficient and granted access to a pyrazole functionalized with an ester group for subsequent deposition of the corresponding tris(pyrazolyl)borate on insulating oxide surfaces. Analytical HPLC confirmed the presence of a mixture of four diastereoisomers.