Abstract

Brominated anthraquinones can be synthesized directly from bromothiophenes when these are reacted with 1,4-naphthoquinones in the presence of meta-chloroperoxy-benzoic acid. The bromoanthraquinones are versatile building blocks in the preparation of arylated anthraquinones and of extended π-systems with interspersed anthraquinone units.

Highlights

  • Arylated anthraquinones 1 (Figure 1) have elicited interest in Physical Organic Chemistry [1,2] due to the interaction of the attached aryl groups with the π-system of the anthraquinone core, as evidenced in the corresponding UV and luminescence spectra [4,5], in the redox behavior of the molecules [2,3], and their NMR shift values

  • A number of synthetic routes to arylated anthraquinones are known. It has been shown by Bergmann et al [7,8] that [4+2]-cycloaddition reactions of phenylbutadienes 2 with either 1,4naphthoquinone (3a) or with p-benzoquinone give 1-phenylanthraquinone (4a) and 1,4diphenylanthraquinone (4b) and 1,5-diphenylanthraquinone and 1,4,5,8tetraphenylanthraquinone, respectively (Scheme 1)

  • Cycloaddition between intermediately formed thiophene S-oxides and 1,4-naphthoquinone 3 takes place, where the formulated, primary sulfoxy-bridged cycloadduct 11 loses the SO-bridge with concomitant aromatization (Scheme 5)

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Summary

Introduction

Arylated anthraquinones 1 (Figure 1) have elicited interest in Physical Organic Chemistry [1,2] due to the interaction of the attached aryl groups with the π-system of the anthraquinone core, as evidenced in the corresponding UV and luminescence spectra [4,5], in the redox behavior of the molecules [2,3], and their NMR shift values. A number of synthetic routes to arylated anthraquinones are known It has been shown by Bergmann et al [7,8] that [4+2]-cycloaddition reactions of phenylbutadienes 2 with either 1,4naphthoquinone (3a) or with p-benzoquinone give 1-phenylanthraquinone (4a) and 1,4diphenylanthraquinone (4b) (from 1,4-naphthoquinone) and 1,5-diphenylanthraquinone and 1,4,5,8tetraphenylanthraquinone (from p-benzoquinone), respectively (Scheme 1). For the preparation of 1,4-diarylanthraquinones, Gautrot et al [2] started from 1,4-dihydroxy-9,10anthraquinone, which was transformed into its bistriflate 5 [3] and subsequently subjected to coupling reaction with arylboronic acids (Scheme 2) [2]. In order to have a versatile strategy to prepare aryl substituted anthraquinones in hand, we wanted to use haloanthraquinones as key intermediates, which we could subsequently transform into the target compounds by Suzuki cross coupling reactions. Indicated that halothiophene S-oxides can be produced in situ and can be reacted with electron poor dienophiles (Scheme 4)

Results and Discussion
Experimental Section
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