Metal-free 5-exo-dig cyclization of propargyl urea using TBAF

We present the first results of the intramolecular cyclization of propargyl ureas catalyzed by TBAF. Depending on the substituents close to the triple bond, imidazolone or methylene-imidazolidinone was obtained. The dual activation of the triple bond by interaction with TBAF via the cation-π is thought to be responsible.

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