Synthesis and stereochemistry of dispiro substituted pyridazines: Application of ellipticity‐absorbance ratio spectra for proving enantiomeric relationship by HPLC‐CD/UV detection

The aim of our study was to synthesize vinylic and pyrido‐fused pyridazines with a spirano moiety and to investigate their stereochemistry by spectroscopic and HPLC analyses. The vinylic compounds 5 were obtained by Knoevenagel condensation of cyclohexylidene malonates 1 with pyridazinecarbaldehyde 2 . Compound 5b exhibits geometric isomerism identified by NMR, HPLC, and X‐ray methods. The thermal rearrangement reactions of compounds 5 easily led to the pyridopyridazine derivatives 6 . In the case of 6b , possessing both central and axial chirality, both diastereomers and the respective enantiomers were detected. Their stereochemical relationships could be determined by HPLC‐CD/UV analyses with application of anisotropy spectra in a novel way. Chirality 14:365–371, 2002. © 2002 Wiley‐Liss, Inc.