Anionen‐induzierte enantioselektive Cyclisierung von Diinamiden zu Pyrrolidinen durch kationische Gold‐Komplexe

Abstract

Zone Fayoum, 63514 (¾gypten) [**] Diese Arbeit wurde großzügig durch die DFG im Rahmen des Emmy-Noether-Programms gefçrdert (CZ 183/1). A.K.M. ist dankbar für ein DAAD-Promotionsstipendium. Dr. Roman Rüttinger wird gedankt für seinen experimentellen Beitrag zur Anwendung chiraler Phosphanliganden (Tabelle 1). Hintergrundinformationen zu diesem Beitrag sind im WWW unter http://dx.

Enantioselective Tandem Cyclization of Alkyne‐Tethered Indoles Using Cooperative Silver(I)/Chiral Phosphoric Acid Catalysis

“…[4] This low number of enantioselective transformations is mainly due to the linear coordination geometry of the ligand-Au-alkyne and the anti addition of Au and an ucleophile across an alkyne.T o address this problem, both well-defined large chiral ligands [5] and the use of chiral counter anions have been studied with some success. [6] Some of these reactions were rendered enantioselective by using other carbophilic catalysts,s uch as iridium, [7] platinum, [5c, 8] palladium, [9] and copper. [10] However, these strategies can only be applied to al imited number of transformations.A lternative approaches for highly enantioselective synthesis of complex carbo-and heterocyclicc ompounds are still in high demand.Inspired by indole alkaloids [11] (see representatives in Figure 1a), our group has developed as eries of cationic gold(I) complex-catalyzed cyclizations of alkyne-tethered indoles (e.g., 1!2,F igure 1b)t oa ccess tetracycilic scaffolds often found in akuammiline alkaloids.…”

Homogeneous Gold‐Catalyzed Cyclization Reactions of Alkynes with N‐ and S‐Nucleophiles

“…Optimization of the reaction conditions revealed that cationic ( t‐ Bu) 3 PAu + with a bulky BINOL phosphate counterion 176 resulted in the best yields and ee s (Scheme ). The catalyst was prepared prior to addition to the reaction, as in situ formation gave inferior the results 119…”

Gold‐Catalyzed Hydrofunctionalizations and Spiroketalizations of Alkynes as Key Steps in Total Synthesis

“…(+)‐Mesembrine, a stimulant originally isolated from the succulent plant Sceletium tortuosum , is a well known standard system to test novel stereoselective methodologies. The Czekelius group envisioned to apply their gold‐catalyzed desymmetrisation reaction for the enantioselective preparation of pyrrolidines with a quarternary stereocenter in 3‐position for the synthesis of the natural compound. While chiral ligands proved unsuccessful, a chiral counter anion strategy delivered the desired pyrrolidines in high enantioselectivities.…”