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The new dienediynes 5, 6, and 7 were synthesised from a monoprotected diyne and an already described bis(enol triflate) 4 derived from formylcyclopentanone. When 5 and 6 were subjected to nucleophilic attack by a thiol, cycloaromatisation occurred, and the phenanthrenes 23a and 23b were obtained in 30 and 42% yield, respectively.
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Suffert et al. (1996) studied this question.
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