Asymmetric Trifluoromethylation of Ketones with (Trifluoromethyl)trimethylsilane Catalyzed by Chiral Quaternary Ammonium Phenoxides

Abstract

Asymmetric trifluoromethylation of ketones with (trifluoromethyl)trimethylsilane catalyzed by cinchonidine-derived quaternary ammonium phenoxides proceeded smoothly to afford the trifluoromethylated compounds in high yields with moderate to high enantioselectivities.

A Copper(I)‐Catalyzed Enantioselective γ‐Boryl Substitution of Trifluoromethyl‐Substituted Alkenes: Synthesis of Enantioenriched γ,γ‐gem‐Difluoroallylboronates

“…Several approaches have been reported that generate ac hiral center at the same time.F or example,t he enantioselective addition of fluorinated nucleophiles to carbonyl compounds is apowerful approach to generate alcohols.Early studies on the enantioselective addition of trifluoromethyl nucleophiles (CF 3 Nu) to carbonyl compounds have been reported by,f or example,F eng, [3] Mukaiyama, [4] and Shibata, [5] and many others. [6] Thee nantioselective addition of difluoromethyl nucleophiles (CHF 2 Nu) to carbonyl compounds is limited to one case reported by Hu and co-workers that proceeded in moderate enantioselectivity (up to 64 % ee).…”

Einführung von Fluor und fluorhaltigen funktionellen Gruppen

“…Chirale, von Cinchona-Alkaloiden abgeleitete Katalysatoren wie 4.5 ermçglichten die asymmetrische Trifluormethylierung aromatischer Aldehyde und Ketone, [398] cyclischer elektroneutraler aromatischer Ketone (Schema 91) [399] und Alkinylketone. [402] Außer Carbonylverbindungen haben sich auch aktivierte Azomethinimine als geeignete Substrate für die enantioselektive Trifluormethylierung mit dem chiralen Ammoniumbromidkatalysator 4.6 erwiesen (Schema 92). [401] Da Kaliumfluorid jedoch schwerlçslich in polaren aprotischen Lçsungsmitteln ist, wurde Phenoxid als Desilylierungsmittel für TMSCF 3 untersucht.…”

New Developments in Chiral Cooperative Ion Pairing Organocatalysis by Means of Ammonium Oxyanions and Fluorides: From Protonation to Deprotonation Reactions.

“…Indeed, one could consider to associate the phenoxide anion with a chiral quaternary ammonium cation through a chiral quaternary ammonium phenoxide ion pair organocatalyst. Such a type of catalyst, even if already described in the literature mainly by the group of Mukaiyama in 2000′s, were then sparingly exploited in the literature. [21],[22] We thus decided to undertake the synthesis of such catalysts and to assess their performances in enantioselective protonation of silyl enol ethers 2 derived from cyclic aromatic ketones (Scheme ) …”