transannular Diels–Alder reaction at room temperature [139] (Scheme 59).
Although the Yamaguchi [89] macrolactonization protocol had been employed in
preliminary studies [140], improved yields were only observed when the reaction
was effected with PyBrOP 201 [130], which was also superior in large-scale
cyclizations.
Scheme 58 BOP-Cl-mediated macrolactonization in the total synthesis of (–)-chlorothricolide,
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Scheme 59 PyBrOP-mediated macrolactonization followed by a transannular Diels–Alder reaction in the racemic synthesis of the enediyne-bridged tricyclic core rac-210 of dynemicin A, 211
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M. Cordes and M. Kalesse