Catalytic, asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with activated olefins by quinidine-derived chiral amines

The chiral nitrogen Lewis base, tricyclic cinchona alkaloid derivative TQO, is an effective promoter in the catalytic, asymmetric aza‐Baylis–Hillman reaction of N‐sulfonated imines Ar? CH?NR′ 1 (R′ = Ts, Ms, Ns, SES) with various activated olefins such as methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), acrolein, methyl acrylate, phenyl acrylate, or α‐naphthyl acrylate to give the corresponding adducts in moderate to good yields with good to high ee (up to 99 %) at ?30 °C or 45 °C in various solvents, including DMF/MeCN (1:1, v/v). The first such reaction of 1 with the simplest Michael acceptor MVK and methyl acrylate has been achieved with excellent enantioselectivity. The adducts derived from MVK and EVK had the opposite absolute configuration to those from acrolein, methyl acrylate, phenyl acrylate, and α‐naphthyl acrylate. A plausible mechanism has been proposed on the basis of previous reports and the authors’ investigations. An effective bifunctional chiral nitrogen Lewis base–Brønsted acid system has been revealed in this type of aza‐Baylis–Hillman reaction.     

Phase-transfer-catalyzed asymmetric Michael reaction using newly-prepared chiral quaternary ammonium salts derived from l-tartrate

The catalytic asymmetric Michael reaction of a glycine Schiff base was demonstrated using new PTCs and moderate to good ee's were achieved (up to 77% ee).     

Chiral Ammonium Betaine‐Catalyzed Highly Stereoselective Aza‐Henry Reaction of α‐Aryl Nitromethanes with Aromatic N‐Boc Imines

A highly stereoselective aza‐Henry reaction of α‐aryl nitromethanes with aromatic N‐Boc imines was established by using C₁‐symmetric chiral ammonium betaine as a bifunctional organic base catalyst. Various substituted aryl groups for both imines and nitromethanes were tolerated in the reaction, and a series of precursors for the synthesis of unsymmetrical anti‐1,2‐diaryl ethylenediamines was provided.     

Enantioselective Aldol Reaction of α-Ketoester and Cyclopentaone Catalyzed by L-Proline

A concise and enantioselective synthesis of (S)‐ethyl 2‐cyclopentyl‐2‐hydroxy‐2‐arylacetate, a key intermediate for the muscarinic receptor, is reported. The tertiary stereogenic center was constructed with good stereoselectivity through the L‐proline‐catalyzed direct asymmetric aldol reaction of ethyl arylglyoxylate and cyclopentanone. The carbonyl of the condensation product was reduced using a modified Clemmensen reaction which provided an easier workup and was more environmentally acceptable. The enantioselectivity of the aldol reactions was between 58.3%–93.2%, which means that the stereoselective is efficient in controlling configuration of reaction product.     

Atropoisomeric (P,N) ligands for the highly enantioselective Pd-catalyzed intramolecular asymmetric α-arylation of α-branched aldehydes

Three-in-one: a short synthetic route readily gives access to a new class of chiral (P,N) ligands characterized by three distinct elements of chirality. These ligands are highly enantioselective in the challenging Pd-catalyzed intramolecular asymmetric α-arylation of α-branched aldehydes.     

Asymmetric Henry reaction catalysed by L‐proline derivatives in the presence of Cu(OAc)2: isolation and characterization of an in situ formed Cu(II) complex

Synthesis of asymmetric β‐nitroalcohols by the Henry reaction is one of the most exploited carbon–carbon bond‐forming reactions owing to the versatility of both functional groups for synthetic manipulation by functional group interconversion. Here we report synthesis of a series of proline‐derived compounds to study their catalytic activities for asymmetric Henry reaction in the presence of Cu(OAc)₂.H₂O. The proline derivative, 2‐((E)‐(((S)‐1‐benzylpyrrolidinyl)diphenylmethylimino)methyl)phenol 1 showed optimum catalytic activity. The catalytic species Cu(II)–1 complex, formed in situ, was isolated and characterized by various spectroscopic techniques and X‐ray crystallography to show a cis‐N₂O₂ coordination geometry. Asymmetric β‐nitroalcohols were achieved without the use of added base, unlike most of the reported protocols. Copyright © 2014 John Wiley & Sons, Ltd.     

Michael-Addition Reaction of Malononitrile with α,β-Unsaturated Cycloketones Catalyzed by KF／Al2O3

A series of KF/Al2O3 catalyzed Michael-addition reactions between malononitrile and α,β-unsaturated cycloketones in DMF solution were studied. At room temperature, 2-cyano-3-aryl-3-(1,2,3,4-tetrahydronaphthalen-1-one-2-yl) propionitrile derivatives were synthesized by the reaction between 2-arylmethylidene-1,2,3,4-tetra-hydronaphthalen-1-one and malononitrile. However, if the temperature was increased to 80℃, 2-amino-3-cyano-4-aryl-4H-benzo[h]chromene derivatives were obtained in high yields. When the α,β-unsaturated ketones were replaced by 2,6-biarylmethylidenecyclohexanone or 2,5-biarylmethylidenecyclopentanone, another series of 2-amino-3-cyano-4H-pyran derivatives was isolated successfully. The structures of the products were confirmed by X-ray diffraction analysis.