Competition Between Oxygen and Nitrogen

In all the examples reported so far, only the nitrogen atom can act as the nucleophile in the intramolecular capture of the seleniranium intermediates. We will 

171 were obtained. During work up, the imidate is easily transformed into the corresponding lactone. The presence of the phenyl group in 172 changes the regiochemistry of the addition reaction and a 6-endo-fng cyclization takes place leading to the 5-lactam 173. The reason is not clear why the endo cyclization of 

The phenylselenyl sulfate promoted cyclization of alkenyl hydroxamic acids reported by Tiecco [98], illustrates the interesting case in which the change of the experimental conditions has a substantial influence on the nature of the 

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