TfOH-Assisted La-Catalyzed Mannich Reaction of g-Butenolides

Significance

This paper describes a highly efficient Mannich-type addition of γ-butenolides to phosphoimines. The use of butenolides in organic synthesis is usually a highly difficult task due to the undesired side reactions. Shibasaki’s group has developed a Lewis acid-Brønsted acid catalytic system that circumvents those difficulties and cleanly catalyzes the reaction. The most interesting point described in this report is the necessity for the Brønsted acid to achieve high yields and selectivities.