Brønsted acid-catalyzed highly stereoselective arene-ynamide cyclizations. A novel keteniminium Pictet-Spengler cyclization in total syntheses of (+/-)-desbromoarborescidines A and C.

[reaction: see text] A Brønsted acid-catalyzed highly stereoselective arene-ynamide cyclization is described. These reactions constitute a keteniminium variant of Pictet-Spengler cyclizations, leading to efficient synthesis of nitrogen heterocycles and related alkaloids. Total syntheses of desbromoarborescidines A and C are illustrated here as first applications of this methodology.