Hydroamination of olefin in a special conjugated spiroketal enol ether system, diastereoselective synthesis of amino-containing tonghaosu analogs

Lithium amide reacted with spiroketal enol ether characterized tonghaosu analog at −78 °C to give the only hydroamination product 4 in a highly regio- and diastereoselective manner. At a higher temperature, −40 °C, the presence of free amine was critical for the hydroamination to take place; otherwise, rearrangement of tonghaosu analog to 2,3-dihydrofuran derivative like 6 was the only reaction.