Fe(III)-Catalyzed Intramolecular Hydroamination of 1,3-Dienes Improved by Using Triphenylphosphate as an Additive

We herein report that the combination of Fe(OTf)3 and triphenylphosphate (TPP, (PhO)3PO) has proven to be an effective catalyst for the intramolecular hydroamination of amino-1,3-dienes with an efficiency and scope superior to previously reported methods. This catalytic system demonstrated consistent performance with diverse aminodienes as well as aminoolefins, providing five- to seven-membered N-heterocycles. We propose a Lewis/Br & oslash;nsted acid cocatalysis mechanism involving proton transfer through hydrogen bonding with TPP. Catalyst system consisting of inexpensive and nontoxic iron salt and phosphate additive, relatively low loading and recyclability of catalyst, and rapid and high-yielding reaction are the advantages of this protocol.