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Synthesis 2006(11): 1819-1822  
DOI: 10.1055/s-2006-942379
PAPER
© Georg Thieme Verlag Stuttgart · New York

Cerium(IV)-Promoted Ethylation of Schiff Bases by Triethylaluminum

Dmitry Tsvelikhovskya, Herbert Schumannb, Jochanan Blum*a
a Department of Organic Chemistry, The Hebrew University, Jerusalem 91904, Israel
Fax: +972(2)6513832; e-Mail: jblum@chem.ch.huji.ac.il;
b Institut für Chemie, Technische Universität, 10623 Berlin, Germany
Fax: +49(30)31422168; e-Mail: schumann@chem.tu-berlin.de;
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Publication History

Received 12 January 2006
Publication Date:
05 May 2006 (online)

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Abstract

Schiff bases Ar1CH=NAr2 that are refractory towards Et3Al are activated at room temperature by cerium(IV) compounds. The ethylation takes place selectively at the methine moiety of the imine. The process is strongly influenced by steric hindrance and depends on the electronic nature of the substrate: electron-donating substituents promote the reaction while electron-withdrawing groups cause it to slow down. Application of cerium(IV) ammonium nitrate as promoter gives the best results. In the absence of excess Et3Al it causes, however, transformation of the Schiff base to the corresponding aldehydes and amines.

Key words

cerium(IV) compounds - C-ethylation - lanthanides, Schiff bases - triethylaluminum