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

Rajkumar Lalji Sahani; Manoj D Patil; Sachin Bhausaheb Wagh; Rai-Shung Liu

doi:10.1002/anie.201806883

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

Angew Chem Int Ed Engl. 2018 Nov 5;57(45):14878-14882. doi: 10.1002/anie.201806883. Epub 2018 Oct 8.

Authors

Rajkumar Lalji Sahani¹, Manoj D Patil¹, Sachin Bhausaheb Wagh¹, Rai-Shung Liu¹

Affiliation

¹ Frontier Research Center for Matter Science and Technology, Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan, ROC.

PMID: 30047589
DOI: 10.1002/anie.201806883

Abstract

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.

Keywords: alkynes; cyclizations; gold; heterocycles; nitrones.