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

Abstract

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 o r N i ( C l O 4 ) 2 • 6 H 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.

Iron(II) complexes of 2,6-di(1-alkylpyrazol-3-yl)pyridine derivatives – The influence of distal substituents on the spin state of the iron centre

“…Alkylation of 3-bpp is achieved by deprotonating preformed 3-bpp with lithium hydride, and reacting the resultant dianion with appropriate alkyl halides [16,32]. The desired N1,N1'-disubstituted products L Me [13], L All [16], L Bz and L iPr were cleanly obtained in each case, with no evidence for competitive alkylation at the pyrazole N2 sites [33].…”

Structure determination of N‐methyl‐tetrahydro‐5H‐indazol‐5‐ones

“…After careful 1 H NMR structural analysis the two N-methyl isomers 1 and 2, the N2-methyl isomer 2 was assigned as the major product. In a similar system of N-methyl menthopyrazoles [8], the N2 isomer is also reported as the major isomer. The H3 proton on 1 and 2 is located at 7.27 and 7.15, respectively ( Figure 1).…”

β‐Protic Pyrazole and N‐Heterocyclic Carbene Complexes: Synthesis, Properties, and Metal–Ligand Cooperative Bifunctional Catalysis

“…A few examples of N-N chelate chiral protic pyrazoles reported so far are shown here. [26,27] X-ray crystallographic studies have revealed that most of these protic pyrazole ligands are associated with hydrogen bonds with Brønsted basic co-ligands, outersphere anions, and solvating molecules, implying the Brønsted acidic nature of the b-NH group. The hydrogen bonds in the solid state are delicately influenced by the ligand substituents and crystal packing.…”