Syntheses of 2H-1-benzothiopyran-2-ones (thiocoumarins) and related compounds from benzenethiols and diketene.
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概要
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The products formed by the reaction of benzenethiols with diketene in the presence of H<SUB>2</SUB>SO<SUB>4</SUB> are (<I>E</I>)-β-(arylthio)crotonic acids (<B>2</B>) and/or isomeric (<I>Z</I>)-β-(arylthio)crotonic acids and not, as has been reported, <I>S</I>-phenyl 3-oxobutanethioates (<B>1</B>). Compounds <B>1a</B>–<B>k</B>, as the precursor of thiocoumarins, were prepared from benzenethiols and diketene in the presence of triethylamine. The reaction of <B>1</B> with various condensing agents has been examined to prepare 2<I>H</I>-1-benzothiopyran-2-ones (thiocoumarins). It is found that 4-methyl(thiocoumarins) were conveniently prepared by the reaction of <B>1</B> with anhydrous aluminium chloride in yields of 16–48%. When <B>1</B> was treated with PPA, isomeric 2-methyl(thiochromones) were preferentially obtained in yields of 5–66%, and compound <B>2</B> was isolated as an intermediate. The spectral characteristics of 4-methyl(thiocoumarins) have also been described.
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