Tricyclic Quaternary Ammonium Salts Derived from Cinchona Alkaloids

Abstract

Tricyclic systems with quaternary bridgehead nitrogen atoms are rare but an interesting class of compounds. Chiral quinuclidine derivative salts with fused five and six-membered rings (X-ray) were obtained via modification of Cinchona alkaloids. The ease of ring formation was dependent on its size, while even mild activation sufficed to close the five membered ring. On the other hand the systems with fused benzene and a six-membered ring formed atropisomers separated by a barrier of ca. 15 kcal/mol, whose interconversion was studied by DFT and NMR.

Synthesis of Both Enantiomers of Chiral Phenylalanine Derivatives Catalyzed by Cinchona Alkaloid Quaternary Ammonium Salts as Asymmetric Phase Transfer Catalysts

“…Although many different methods for the synthesis of α-phenylalanine derivatives have been reported in the literature [ 10 , 11 , 12 ], these methods have significant drawbacks, such as the use of very costly catalysts, low yields, and/or poor enantioselectivity for some derivatives. Asymmetric phase-transfer catalysis has been widely used for the synthesis of chiral α-amino acids because of its operational simplicity, mild reaction conditions, and reduced environmental impact [ 13 , 14 , 15 , 16 , 17 ]. Quaternary cinchona alkaloid catalysts, discovered by O’Donnell et al .…”