Catalytic Transformations of Alkynes into either α‐Alkoxy or α‐Aryl Enolates: Mannich Reactions by Cooperative Catalysis and Evidence for Nucleophile‐Directed Chemoselectivity

• Published in: Angewandte Chemie International Edition 2018-11, Vol.57 (45), p.14878-14882
• Main Authors: Sahani, Rajkumar Lalji, Patil, Manoj D., Wagh, Sachin Bhausaheb, Liu, Rai‐Shung
• Format: Article
• Language: English
• Subjects: Alkynes; Aromatic compounds; Bonding; Catalysis; cyclizations; Gold; heterocycles; Imines; nitrones; Nucleophiles
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201806883

The catalytic formation of gold enolates from alkynes, nitrones, and nucleophiles is described, and their Mannich reactions result in nucleophile‐directed chemoselectivity through cooperative catalysis. For 1‐alkyn‐4‐ols and 2‐ethynylphenols, their gold‐catalyzed nitrone oxidations afforded N‐containing dihydrofuran‐3(2H)‐ones with syn selectivity. The mechanism involves the Mannich reactions of gold enolates with imines through an O‐H‐N hydrogen‐bonding motif. For aryloxyethynes, their gold enolates react selectively with nitrones to deliver 3‐alkylidenebenzofuran‐2‐ones, as controlled by a C‐H‐O hydrogen‐bonding motif. ’Syn'tax: Reported is the catalytic formation of gold enolates from alkynes, nitrones, and nucleophiles. The resulting Mannich reactions result in nucleophile‐directed chemoselectivity derived from cooperative catalysis. For 1‐alkyn‐4‐ols and 2‐ethynylphenols, their gold‐catalyzed nitrone oxidations afforded N‐containing dihydrofuran‐3(2H)‐ones with syn selectivity, and for aryloxyethynes, 3‐alkylidenebenzofuran‐2‐ones are delivered.