Enantioselective Carbonyl‐Ene Reactions of Trifluoropyruvate in Ionic Liquid via a Recyclable Indium(III)‐Pybox Complex

Abstract

A highly enantioselective carbonyl-ene reaction of trifluoropyruvate catalyzed by a recyclable indiumA C H T U N G T R E N N U N G (III)-pybox complex in ionic liquid afforded trifluoromethyl-containing tertiary homoallylic alcohols with excellent yields (up to 98%) and enantioselectivities (up to 98% ee). Notably, this catalytic system can be recycled up to seven cycles.

The Future of Catalysis by Chiral Lewis Acids

“…A broad spectrum of chiral Lewis acid catalysts has been used for the carbonylene reaction, and recent examples show the adaptability of this transformation to recycling (Scheme 29) in an ionic liquid [132], to very low catalyst loadings (Scheme 30) in magnetic nanoreactors [133], as well as to the uses of unconventional asymmetric catalysts that include those of palladium(II) with C 2 -bridged chiral diphosphine ligands [134], NCN pincer rhodium(III) catalysts [135], and chiral cationic dirhodium(II,III) [136]. An intramolecular carbonyl-ene reaction has also been shown to produce polycyclic products in high yield and stereocontrol Scheme 27 Intermolecular [2+2] reaction of N-allenyl sulfonamides with vinyl arenes [125] The Future of Catalysis by Chiral Lewis Acids that were previously formed by cationic polyene cyclization (Scheme 31), thus opening a new synthetic methodology for the stereoselective synthesis of polycyclic compounds [137].…”

“…Scheme 29 Enantioselective carbonyl-ene reaction of trifluoropyruvate [132] Scheme 30 Enantioselective carbonyl-ene reaction on BINOLate/titanium catalyst encapsulated in magnetic nanoreactors [133] Scheme 31 Enantioselective cationic polyene cyclization of α-ketoester [137] Scheme 32 Highly enantioselective carbonyl-ene reactions of 2,3-diketoesters [138] Q. Sha et al With the substituent R being a broad spectrum of structures and functional groups, the potential of these enophiles to broaden the applicability of the carbonyl-ene reaction in organic synthesis is high.…”

Ionic Liquids in Asymmetric Synthesis: An Overall View from Reaction Media to Supported Ionic Liquid Catalysis

“…In 2010, Loh and his group reported the carbonyl-ene reaction of trifluoropyruvate catalyzed by indium(III)-pybox complex 25 in [Hmim][PF 6 ]i onic liquid (Scheme 17). [76] Trifluoromethyl-containing homoallylic alcohols, which are important buildingb locks owing to their unique properties (lipophilicity, stability, and high electronegativity of the CF 3 group [77] ), are produced in excellent yields (up to 98 %) with excellent enantioselectivities (up to 98 % ee). The authors use, for the first time, ionic liquidsa sr eaction media in ab iphasic system (ionic liquid/1,2-dichloroethane) fort his transformation.T he ionic liquidsf acilitate isolation of the products by simple extraction.…”

Applications of Pybox Complexes in Asymmetric Catalysis

“…Loh and co-workersa lso developed ar ecyclable In III -Pybox complextocatalyse the enantioselective carbonyl-ener eaction of trifluoropyruvate, which was performed in an ionic liquid (Scheme 40). [44] The best results were obtained if 10 mol % InCl 3 ,2 0mol %A gSbF 6 ,1 2mol %( + +)-3 and 4 molecular sieves were used in [hmim][PF 6 ]/1,2-dichloroethane at room temperature. The presence of an EWG on the phenylr ing of the substituted a-methylstyrene prolonged the reaction time, whereas an EWG or EDG at the ortho positionl ed to lower yields and ee,p resumably owing to steric effects.…”