Preparation of 2,6‐bis( l ‐menthopyrzol‐3‐yl)pyridines and their catalytic activity for asymmetric diels alder reaction

3‐Aryl‐ l ‐menthopyrazoles 1 and 2 and related compounds were prepared from l ‐menthone, and their enantioselective activities were discussed as chiral ligands. In this series of compounds, 2,6‐bis(2‐methyl‐ l ‐menthopyrazol‐3‐yl)pyridine ( 8a ), which had both structural features of 3‐phenyl‐ l ‐menthopyrazole ( 1b ) and C 2 symmetric ligand in the molecule, should form the C 2 symmetric complex in situ with Zn(OTf) 2 or Ni(ClO 4 ) 2 •6H 2 O. The subsequent complex catalyzed the Diels Alder reaction of 1‐acryloyl‐3,5‐dimethylpyrazole ( 11a ) with cyclopentadiene ( 12 ) enantioselectively up to 75 % ee.