Issue in Honor of Prof. Keith Smith ARKIVOC 2012 (vii) 274-281
Functionalization of naphthalene: a novel synthetic route to brominated naphthoquinones
Osman Cakmak,a* Kiymet Berkil Akar,b and Nuri Kaplana
a Department of Chemistry, Faculty of Art and Science, Gaziosmanpasa University, 60250 Tokat, Turkey b Department of Bioengineering, Faculty of Engineering and Natural Science, Gaziosmanpasa University, 60250 Tokat, Turkey E-mail:
[email protected]
Dedicated to Professor Keith Smith on the occasion of his 65th anniversary
Abstract An efficient procedure is described for synthesis of 2,5,8-tribromonaphthoquinone (12) from naphthalene in four reaction steps. Silver-promoted solvolysis of hexabromide 3 produces the specific diastereostereoisomer 10. Dehydrobromination of 10 using sodium methoxide gives tribromodihydronaphthalene-1,4-diol 11 in high yield. PCC oxidation of either 10 or 11 results in the formation of 2,5,8-tribromonaphthalene-1,4-dione (12).
Keywords: Bromonaphthalene, bromination, silver-induced substitution, 1,4-naphthoquinone, PCC oxidation
Introduction
The naphthoquinone structure exists in many natural products and biologically active compounds.1 Among the naphthaquinones, 2-substituted-1,4-naphthoquinone derivatives are especially interesting molecules because of the their extremely important biological activities, such as antibacterial,2 antitrypanosomal,3 antileishmanial,3 molluscicidal,4 cytotoxic5 and antitumor6 properties.
Naphthoquinones are industrially used as raw materials for pharmaceuticals, agrochemicals and other chemicals.7 Therefore, development of novel synthetic methodologies for the synthesis of naphthoquinones is an important task for chemists.8
Our studies have shown that bromination conditions dramatically affect the regio-and stereo- selectivity of bromination reactions.9 Different products are obtained depending on both the structures of the starting materials and the reaction conditions. For example, while
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