Pyrrolidine-Based Chiral Quaternary Alkylammonium Ionic Liquids as Organocatalysts for Asymmetric Michael Additions

Abstract

A series of chiral pyrrolidine-type quaternary alkylammonium ionic liquids were synthesized and served as efficient catalysts for asymmetric Michael additions of aldehydes and ketones to nitroolefins, and the corresponding adducts were obtained in excellent enantioselectivities ([99% ee) and diastereoselectivities ([99% dr) under solvent-free reaction conditions. Furthermore, the catalyst 7c could be recovered for next run of the reaction with similar yield and selectivity.

Asymmetric Michael Additions Catalysed by Functionalised Quaternary Alkylammonium Ionic Liquids

“…It was reported that acidic additives exhibited important impact on the yield and enantioselectivity of the reaction catalysed by compound 1c. 23 But when 8b was used as a catalyst of the Michael reaction, a similar stereoselectivity to TFA was obtained in the presence of AcOH, CH 3 SO 3 H and p-TsOH (entries 7-9). Also the reaction yield in the presence of CH 3 SO 3 H was lower than that of TFA, AcOH and p-TsOHFinally, it was found that the Michael reaction could proceed without acidic additive to afford similar results (Entry 10).…”

“…General experimental procedure for the Michael addition of cyclohexanone to nitroalkene by chiral catalyst: TFA (2.85 mg 0.025 mmol) was dropped into a solution of the chiral catalyst (0.075 mmol) in cyclohexanone (1g, 10mmol). 23 After stirring for 1 h, nitroalkene (0.5 mmol) was added, and the solution was stirred at r.t. until nitroalkene had disappeared by Analytical TLC (EA: PE = 1:5). The solution was diluted with water (5 mL), and the resulting mixture was extracted with EA (2 mL×3).…”

“…(0.9 g, 48% yield);1 H NMR (500 MHz, D 2 O) δ ppm: 0.96-1.20 (6H, m), 1.75-1.79 (3H, m), 2.00-2.05 (1H, m), 2.52 -2.89 (6H, m), 3.06-3.14 (2H, m), 3.17-3.41 (4H, m), 4.21 (1H, s), 4.92-5.06 (2H, m), 7.26-7.29 (5H, m). Synthesis of the intermediate 7b: Under N 2 protection, intermediate 6 (1.6 g 6.2 mmol) and MeCN (12 mL) were added to a single neck bottle 23. After 6 had dissolved, 1-bromo-2-methylpropane (3.2 g 0.023 mol) was added.…”

Asymmetric Michael Addition Mediated by Chiral Ionic Liquids

“…Studies related to the synthesis of proline-derived chiral ionic liquids with onium moieties other than imidazolium and their use in asymmetric Michael addition reactions have been published. 1-(Pyrrolidin-2-ylmethyl)pyridinium ionic liquid 44 has been reported by Headley and his co-workers (Scheme 18 ) [ 45 ], and alkyl ammonium ionic liquids bearing N -pyrrolidin-2-ylmethyl group 45 and 46 have been reported by Wang’s group (Scheme 19 ) [ 46 ] and Chen’s group (Scheme 20 ) [ 47 ], respectively.…”

An Ionic Liquid Containing L‐Proline Moiety as Highly Efficient and Recyclable Chiral Organocatalyst for Michael Addition

“…Especially, some ionic liquids as simple recyclable chiral catalyst have opened an access for highly enantioselective reactions . Recently, it was reported that the ionic liquid‐supported proline or pyrrolidine derivatives were successfully used in the Michael addition of ketones and aldehydes to nitroolefins, affording the products in high yields and excellent stereoselectivities. These supported catalysts can be recovered by magnetic field or precipitation with diethyl ether.…”