Cooperative Rh/Chiral Phosphoric Acid Catalysis toward the Highly Stereoselective (3 + 3)-Cycloannulation of Carbonyl Ylides and Indolyl-2-methides.

A stereoselective (3 + 3)-cycloannulation of in situ generated carbonyl ylides with indolyl-2-methides has been developed furnishing oxa-bridged azepino[1,2-a]indoles within one synthetic step. This process is enabled by cooperative rhodium and chiral phosphoric acid catalysis to produce both transient intermediates in separate catalytic cycles. The products comprising three stereogenic centers were obtained with good stereoselectivity and yields and display valuable heterocyclic complexity.