Highly enantioselective asymmetric Darzens reactions with a phase transfer catalyst

Abstract

A class of easily accessible and readily tunable chiral phase transfer catalysts based on 6’-OH cinchonium salts was found to efficiently catalyze an unprecedented highly enantioselective Darzens reaction of α-chloro ketones and aldehydes, which directly produces optically active chiral epoxides from readily available carbonyl compounds.

Structural Study‐Guided Development of Versatile Phase‐Transfer Catalysts for Asymmetric Conjugate Additions of Cyanide

“…[11] These attempts have so far been met with limited success. Our recent development of cupreinium salts 1 , as highly enantioselective phase transfer catalysts for an asymmetric Darzens reaction, [12] prompted us to explore them for the asymmetric conjugate addition of cyanide. Similar to other known bifunctional phase transfer catalysts bearing a hydrogen bond donor moiety, [13],[14],[15] cupreidinium salts CPD- 1 , could in principle mediate phase transfer catalysis by their association with an anionic cyanation species, presumably a cyanide or cyanoalkoxide, via simultaneous ion-pair and hydrogen bonding interactions ( I , Figure 1).…”

Catalytic Asymmetric Darzens and Aza‐Darzens Reactions for the Synthesis of Chiral Epoxides and Aziridines

“…Cinchona alkaloids containing hydrogen bond donors other than aliphatic alcohols have led to great strides in chiral‐acid‐base cooperative catalysts, and the corresponding chiral ammonium salts derivatives could potentially be employed as effective phase‐transfer catalysts. Based on this principle Deng et al . reported a catalytic asymmetric DR between α‐chloro acyclic and cyclic ketones and aliphatic and aromatic aldehydes mediated by 3,4,5‐trifluorobenzyl‐incorporated 6′‐OH cinchona alkaloids PTC 12 .…”

Neue Entwicklungen bei asymmetrischen Phasentransferreaktionen

“…166, mit Aldehyden und dem Katalysator 1 r beschrieben, wobei die 9-Phenanthracenyl-und die 6'-Hydroxygruppe des Katalysators für die hohe Enantioselektivität ausschlaggebend waren (Schema 103). [133] Auch Bakó et al berichteten über die asymmetrische Darzens-Reaktion mit dem chiralen Azakronenether 119 b, die das Produkt mit mittlerer Enantioselektivität ergab (Schema 103). [134] Schema 99.…”