Lanthanide (III) salt complexes: Arrayed acid‐base networks for enantioselective catalysis. The nitroaldol reaction upon aldehydes and trifluoromethylketones

Abstract

Shelf stable, chiral-at-metal, D(3) symmetric, 3:1 complexes of lanthanide (III) triflate salts are easily available by complexation with binolam (3,3'-diethylaminomethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 1 or binolamo (3,3'-diethylaminooxymethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 2 ligands. The resulting compounds 3Ln and 4Ln are isostructural, as demonstrated by their spectroscopic data, and possess an arrayed acid-base LABABB network. Complexes are kinetically labile, and in solution undergo hydrolysis by water. The lanthanum complex derived from binolam, i.e., (Delta,S,S,S)- (binolam)(3).la(OTf)(3)3La was found to be the most active catalyst in promoting direct nitroaldol reactions upon aldehydes and trifluoromethyl ketones, thereby giving rise to secondary nitroalcohols and tertiary alpha-trifluoromethyl-beta-nitroalcohols, respectively, with high ee in both cases. Enantiomerically enriched tertiary nitroalcohols were easily reduced to the corresponding aminoalcohols having a quaternary asymmetric carbon without loss of enantiomeric purity.

[Ln(binolam)3]⋅(OTf)3, a New Class of Propeller‐Shaped Lanthanide(III) Salt Complexes as Enantioselective Catalysts: Structure, Dynamics and Mechanistic Insight

“…The N‐oxide derivative of ligand 1 , binolamo 7 , has also been shown to be capable of forming the interesting series of complexes [Ln(binolamo) 3 ] ⋅ (OTf) 3 , closely related to those derived from binolam, for which no applications in asymmetric catalysis have yet been reported. Herein, we report only the scandium complex 8 , useful for our purposes in the structural investigation 11…”

Asymmetric Henry Reaction of Trifluoromethyl Enones with Nitromethane Using a N,N‐Dibenzyl Diaminomethylenemalononitrile Organocatalyst

“…Thus, asymmetric Henry reactions using metal catalysts and organocatalysts were reported by several research groups [8,9] . However, reports on asymmetric Henry reactions with α,β‐unsaturated trifluoromethyl ketones are rare and only those using trifluoromethyl ynones as a substrate are commonly available [8a,b,10] . Furthermore, to the best of our knowledge, there are still no reports available on regarding the asymmetric Henry reaction with trifluoromethyl enones (e. g., ( E )‐1,1,1‐trifluoro‐4‐phenylbut‐3‐en‐2‐one) in spite of the significant value of the products such as chiral synthons.…”

Constructing Quaternary Centers of Chirality: The Lanthanide Way to Trifluoromethyl-Substituted Tertiary Alcohols

“…be stored for months without deterioration, and their structure has been fully established. 97 An initial exploration of their capabilities as enantioselective catalysts for the nitroaldol reaction in organic solvents showed that the (Binolam) 3 Ln(OTf) 3 (4Ln) catalysts were more efficient than the (Binolamo) 3 Ln(OTf) 3 (5Ln) catalysts. Among the former group of catalysts, the lanthanum derivative (S)-(Binolam) 3 La(OTf) 3 (4La) was the catalyst of choice.…”