Synthesis, molecular structure, and complexation of 1,4-dihydropyridines containing ligands for intramolecular complexation of metal electrophiles

✍ Scribed by Bernard Kaptein; Richard M. Kellogg; F. van Bolhuis

• Book ID: 104589201
• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 749 KB
• Volume: 109
• Category: Article
• ISSN: 0165-0513
• DOI: 10.1002/recl.19901090605

✦ Synopsis

Abstract

A series of 4‐substituted Hantzsch 1,4‐dihydropyridines has been synthesized. Substituents at the 4‐position include 2‐pyridyl, 2‐imidazolyl, and 1‐methyl‐2‐imidazolyl. By use of various acetoacetic ester derivatives methoxy and methylthio groups have been introduced in the ester side chains at the 3,5‐positions. A representative example is bis(2‐methoxyethyl) 1,4‐dihydro‐2,6‐dimethyl‐4‐(1__H__‐imidazol‐2‐yl)‐3,5‐pyridinedicarboxylate (5h). The crystal structure of bis‐[(2‐methylthio)ethyl] 1,4‐dihydro‐2,6‐dimethyl‐4‐(1__H__‐imidazol‐2‐yl)‐3,5‐pyridinedicarboxylate (5i) has been determined. The imidazole group at the 4‐position is located in a pseudo‐axial position. In the ^13^C‐ and ^1^H‐NMR spectra line doubling is seen in the 4‐imidazole‐substituted derivatives. This is apparently the result of slow tautomerization. Various complexes with Zn(NO~3~)~2~ · 4H~2~O have been prepared but no crystal structures could be obtained. These 1,4‐dihydropyridines have little capacity, either in the presence or absence of metal ions, to carry out reductions. This may be the result of a stereoelectronic effect caused by the (presumably) equatorial orientation of the hydrogen (hydride) to be donated.