Gold-Catalyzed Heteroannulation Route of N-Allyl Ureas to Tricyclic Indolines

Significance

In the continuation of their research in gold-catalyzed oxidative cross-coupling reactions (e.g., coupling of alkylgold compounds with arylboronic acids: G. Zhang, L. Cui, Y. Wang,
L. Zhang J. Am. Chem. Soc. 2010, 132, 1474), Zhang and co-workers studied the possibility of replacing the Csp^²-boron reagents by corresponding simple and economical Csp^²-H substrates. Herein, the Au(I)/Au(III)-catalyzed synthesis of tricyclic indolines 2 is reported from N-allyl urea 1 via 5-exo-trig aminoauration followed by intramolecular [3+2] annulation. Mechanistic studies using deuterium labeling, kinetic isotope effect, and isolation of alkylgold intermediates support an electrophilic aromatic auration followed by concerted reductive elimination to form the Csp^²-Csp^³ bond to give product 2.