Molecular structures of regioisomeric 7‐arylidene hexahydroindazoles from ¹H NMR spectra

Abstract

The structural characterization of two regioisomeric products of the interaction of 2,6-bis-(4-methoxybenzylidene)-3R-methylcyclohexanone with methyl hydrazine was achieved using (1)H NMR spectral data, including chemical shifts, coupling constants and results of COSY and nuclear overhauser effect (NOE) experiments. Configurations of the new chiral centers in the (3S,3aR,6R,7E)-7-(4-methoxybenzylidene)-3,4,5,7-hexahydro-3-(4-methoxyphenyl)-2,6-dimethyl- and 2,4-dimethyl-2H-indazoles were assigned on the basis of experimental data combined with molecular modeling by the density functional theory (DFT) method. The distinction in the helical twisting power of studied compounds under addition to a nematic liquid crystal is discussed on the basis of peculiarities of the molecular structures.

New chiral 3-aryl-7-arylmethylidene-3,3a,4,5,6,7-hexahydroindazoles: Synthesis, structure, and twisting power in nematic liquid crystals

“…The twisting power was measured in 4′-pentylbiphenyl-4-carbonitrile according to the procedure described in [24]. (3S,3aR,6R,7E)-7-(4-Methoxybenzylidene)-3-(4-methoxyphenyl)-2,6-dimethyl-3,3a,4,5,6,7-hexahydro-2H-indazole (IIIb) and (3S,3aR,4R,7E)-7-(4-methoxybenzylidene)-3-(4-methoxyphenyl)-2,4-dimethyl-3,3a,4,5,6,7-hexahydro-2H-indazole (IVb) were synthesized according to the procedure described previously [14].…”

“…We considered compounds III and IV as target components of liquid crystalline compositions. They were synthesized under conditions of base catalysis using triethylamine (in the synthesis of IIIb) [14] or excess methylhydrazine (IIIa-IIIe) to avoid tarring in acid medium. In the general case, the reaction with methylhydrazine gives two groups of regioisomeric products III and IV (Scheme 1), depending on the double bond (C 2 =C or C 6 =C) involved in the formation of pyrazole fragment; in addition, cis-trans isomerism with respect to the C 3 -C 3a bond is possible; therefore, eight regio-and stereoisomers may be formed.…”