Ring internal formyl group

Scheme 5.108 Ring-closing hydroaminomethylation with an internal formyl group.

Although the mechanism of the Dakin reaction given in many textbooks does not involve participation of the n electron of the aromatic ring, the mandatory presence of polar substituents (e.g., OH) in the ortho or para position to the formyl group suggests that an internal electrophilic substitution of the adduct intermediate is a better representation. The uncatalyzed S Ar process is a soft-soft interaction. 

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