Nucleophile-vinyl cation reaction intramolecular cyclization

Rychnovsky reported synthesis of Leighton s macrolide 201 of leucascandrolide A, wherein the key reaction is the Mukaiyama aldol-Prins cascade reaction (Sect. 2.4). In this cascade reaction, oxonium cation, required for the Prins reaction, is prepared by a Lewis acid-mediated Mukaiyama aldol reaction of alkyl vinyl ether with aldehyde. Usually, alkyl vinyl ethers are not suitable for Mukaiyama-aldol, because of oligomerization of the resulting oxonium cation. Rychnovsky resolved this issue by trapping the cation with an intramolecular nucleophile, which resulted in Prins cyclization. 

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