Abstract

Synthesis of p-phenylthio- peri-hydroxy polyaromatic compounds by strong-base-induced [4+2] cycloaddition of 4-(phenylthio)homophthalic anhydrides with phenylsulfinyl- dienophiles

Highlights

  • We briefly reported a third method, based on the strong-base-induced [4+2] cycloaddition of 4-(phenylthio)homophthalic anhydrides (1a,b) to sulfinyl-substituted dienophiles, in which we found that the sulfinyl groups were essential for producing the desired reaction under mild conditions in good yields (Scheme 1)

  • A reaction mechanism to explain the remarkable effect of the sulfinyl group is discussed

  • In order to establish the regioselective synthesis of the p-phenylthio-substituted peri-hydroxy polyaromatic compounds, we examined the strong-base-induced [4+2] cycloaddition of 1a with naphthoquinones (5a–d) bearing various types of activating groups (X)

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Summary

Introduction

General and efficient syntheses of peri-hydroxy polyaromatic p-quinones (I) and their dihydroquinone derivatives (II) are important in recent synthetic organic- and medicinal chemistry because these compounds are key components of many biologically important natural products such as anthracyclines and fredericamycin A.2 For the synthesis of these quinone compounds, the transformation of phenols into p-benzoquinones or p-dihydrobenzoquinone derivatives has been one of the most important steps. Recently, we reported a new method for the synthesis of I and II from p-(phenylthio)phenols (III) via the aromatic Pummerer-type reaction of the derived sulfoxides (IV). The synthesis of III has been achieved by two methods; viz, the p-specific thiocyanation of phenols (V) using the combination of PhICl2 and Pb(SCN). For the synthesis of these quinone compounds, the transformation of phenols into p-benzoquinones or p-dihydrobenzoquinone derivatives has been one of the most important steps.. We reported a new method for the synthesis of I and II from p-(phenylthio)phenols (III) via the aromatic Pummerer-type reaction of the derived sulfoxides (IV).. Followed by reaction with PhMgBr (method A)4d,5 and the oxidative intramolecular [4+2] cycloaddition of o-[(ω-phenylthio-ethynyl)acyl]-phenols (VI) (method B).. We briefly reported a third method, based on the strong-base-induced [4+2] cycloaddition of 4-(phenylthio)homophthalic anhydrides (1a,b) to sulfinyl-substituted dienophiles, in which we found that the sulfinyl groups were essential for producing the desired reaction under mild conditions in good yields (method C) (Scheme 1).. We give a full account of our studies on method C, with additional examples using the new homophthalic anhydrides (1c and 1d). A reaction mechanism to explain the remarkable effect of the sulfinyl group is discussed

Results and Discussion
H H OMe OMe
Conclusions

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