One-pot synthesis of 4'-alkyl-4-cyanobiaryls on the basis of the terephthalonitrile dianion and neutral aromatic nitrile cross-coupling.

Roman Yu Peshkov,Wang Chunyan,Evgeny V Tretyakov,Vitalij D Shteingarts,Elena V Panteleeva

doi:10.3762/bjoc.12.153

Abstract

A convenient one-pot approach to alkylcyanobiaryls is described. The method is based on biaryl cross-coupling between the sodium salt of the terephthalonitrile dianion and a neutral aromatic nitrile in liquid ammonia, and successive alkylation of the long-lived anionic intermediate with alkyl bromides. The reaction is compatible with benzonitriles that contain methyl, methoxy and phenyl groups, fluorine atoms, and a 1-cyanonaphthalene residue. The variety of ω-substituted alkyl bromides, including an extra bromine atom, a double bond, cyano and ester groups, as well as a 1,3-dioxane fragment are suitable as alkylation reagents.

Highlights

Alkylcyanobiphenyls are well known largely due to their mesogenic properties, which were discovered by Gray in the 1970th [1,2]
The reaction proceeds under evaporating ammonia at −33 °C, and it does not need an additional source of inert atmosphere for the overall reaction time, which is ca. 3 h
The reaction mixtures obtained, along with target alkylcyanobiaryls 5, contain starting materials 1, 2, and several byproducts, such as 4-alkylbenzonitriles 7, 1-alkylcyclohexa-2,5-dienecarbonitriles 8, and alkylbenzenes 9

Summary

Introduction

Alkylcyanobiphenyls are well known largely due to their mesogenic properties, which were discovered by Gray in the 1970th [1,2]. Scheme 2: Para-cyanophenylation of substituted benzonitriles 2 by dianion 12− with the formation of a long-lived cyanocyclohexadienyl anion 3, followed by oxidation or alkylation, leading to dicyanobiphenyls 4 or alkylcyanobiphenyls 5.

Results

Conclusion