Counter-rotatable dual cinchona quinuclidinium salts and their phase transfer catalysis in enantioselective alkylation of glycine imines

Abstract

Dual cinchona quinuclidinium salts with a diphenyl ether linker were synthesized and used as powerful asymmetric phase transfer catalyst in the α-alkylation of imines of glycine and alanine ester with...

New Trends in Asymmetric Phase Transfer Catalysis

“…More recently, similar dimeric catalysts 4 with a diphenyl ether/thioether linker could provide excellent results with a significantly lower catalyst loading in the range of 0.01–0.05 mol% (Scheme 3). [21] …”

“…[20] More recently, similar dimeric catalysts 4 with a diphenyl ether/ thioether linker could provide excellent results with a significantly lower catalyst loading in the range of 0.01-0.05 mol% (Scheme 3). [21] Moreover, a slight excess only of the alkylation agent was used and the size of the ester did not influence the yield and the stereoselectivity.…”

Enantioselective Alkylation of Glycine Imines Using a Cinchona-Functionalized Crown Ether-Strapped Calixarene Phase-Transfer Catalyst

“…The asymmetric phase transfer catalytic process is very attractive due to the simple and mild reaction conditions with quaternary ammonium salts as the PTC . Since Dolling reported the first enantioselective phase-transfer-catalyzed asymmetric α-alkylation of indanones using a pseudoenantiomeric Cinchona alkaloid-derived quaternary ammonium salt, α-alkylation of glycinate imines has seen a resurgence of activity along with other enantioselective [4 + 1] annulation, N -alkylation, conjugate addition, fluorination, and Mannich reactions . Impressive advances have been made toward the development of photoswitchable azo-crown ether-, dimeric cinchonidinium-, spirocyclic ammonium-, and phosphonium salt-mediated PTCs for α-alkylation of glycine imines, even though high enantioselectivities have been realized only for limited substrates .…”