Heterocyclic 3,5-disubstituted phenylpyrazoles and isoxazoles: Synthesis and mesomorphic behavior

Hsiu Ming Kuo, Shao Ling Tsai, Gene Hsiang Lee, Hwo Shuenn Sheu, Chung K. Lai

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17 Scopus citations

Abstract

Three new series of heterocyclic pyrazoles Mpz-Cn and Epz-C n and isoxazoles Iz-Cn were prepared, characterized, and their mesomorphic properties investigated. These heterocyclic derivatives were obtained by condensationecyclization of β-diketones with methylhydrazine, 2-hydradinoethanol or hydroxylamine in refluxing THF/ethanol. One single crystallographic structure of nonmesogenic Epz-C4 was determined by Xřay analysis. It crystallizes in a triclinic space group P-1. An H-bond-induced structure was formed, giving a better aspect ratio required for the formation of mesophases. Both series of pyrazoles Mpz-Cn and EpZ-Cn exhibited monotropic smectic A phases, in contrast, isoxazoles Iz-Cn formed enantiotropic smectic C phases. A lack of H-bond due to a removal of hydrogen atom from pyrazolyl rings (-NH) significantly lowered the clearing temperatures of both Mpz-Cn and EpZ-Cn. These compounds have good thermal stabilities.

Original languageEnglish
Pages (from-to)618-626
Number of pages9
JournalTetrahedron
Volume69
Issue number2
DOIs
StatePublished - 14 Jan 2013

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