Synthesis 2009(10): 1753-1756  
DOI: 10.1055/s-0028-1088049
PSP
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of 3,6-Dimethoxybenzene-1,2-diamine and of 4,7-Dimethoxy-2-methyl-1H-benzimidazole

Tatiana Besset, Christophe Morin*
Département de Chimie Moléculaire (CNRS, UMR-5250, ICMG FR-2607), Université Joseph Fourier, 301 rue de la chimie, BP 53, 38041 Grenoble Cedex 9, France
Fax: +33(4)76635983 ; e-Mail: [email protected];
Further Information

Publication History

Received 11 December 2008
Publication Date:
14 April 2009 (online)

Abstract

Hydrogenation of a mixture of ortho- and para-dinitro derivatives of 1,4-dimethoxybenzene in ethyl acetate under palladium catalysis, allows 3,6-dimethoxybenzene-1,2-diamine to be isolated as the sole product; this diamine is then converted into 4,7-dimethoxy-2-methyl-1H-benzimidazole, a building block for the preparation of imidazobenzo(hydro)quinones.

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8

Ref. 7 reads that this is a co-crystallization process and that, provided there are no ‘small aggregates’, the separation of ‘rhombic plates’ from ‘long columns’ can be effected by hand.

9

The ratio of isomers is determined by relative integration in ¹H NMR spectra, for data see experimental.

10

The mp recorded for this material is in the range of literature values (68-70 ˚C,4e 75 ˚C,² 85-87 ˚C4a). Note that this material is labile: darkening with time of this electron-rich diamine has been noted previously and we found experimentally that even after minimal exposure to air, 1 became unreactive.

11

A H2-filled balloon is used, monitoring of the reaction can be performed by TLC or NMR (for data see experimental) but, most simply, it can be done by visual inspection as the mixture becomes colorless when reaction is complete.

12

Hydrogenation of a 6:4 mixture of 3 and 4 was performed under the same protocol and, here also, only diamine 1 is isolated (51% yield; 85% based on 3).

15

Impure 2 could not be freed from byproducts by crystallization or by chromatography, which furthermore led to severe losses of material.