S. G. Zlotin

Asymmetric organocatalysis: from proline to highly efficient immobilized organocatalysts*

The recent results of the authors’ research group on the application of chiral ionic liquids and related compounds as recoverable organocatalysts of asymmetric reactions are reviewed.

Bis(tetrazolyl)benzenes as ligands in the Suzuki reaction: Promoters or inhibitors?

The Suzuki cross-coupling with phenylboronic acid in the presence of the Pd(OAc)2/K3PO4/DMF catalytic system was successful for aryl bromides and somewhat poorer for aryl chlorides. Addition of 1,3-bis(tetrazol-1-yl)benzene or its analogs lowered the yields of biaryls.

Cross-coupling of polychloroarenes with phenylboronic acid and organozinc compounds catalyzed by palladium complexes

Hexachlorobenzene and 1,2,4,5-tetrachlorobenzene react with phenylboronic acid by a C—C cross-coupling mechanism with a Pd(dba)2/P(But)3 system (dba is dibenzylideneacetone) or palladium-azole complexes as catalysts, or with organozinc compounds in the presence of Pd(PPh3)4 to afford substitution products of one or two chlorine atoms in moderate yields.

Reaction of aromatic aldehydes with β-dicarbonyl compounds in a catalytic system: Piperidinium acetate-1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Condensation of aromatic (heteroaromatic) aldehydes with 1,3-dicarbonyl compounds under the 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) ionic liquid-piperidinium acetate catalytic system (0.2 equiv. of each component) in the absence of a solvent affords, depending on the structures of the reagents, 2-arylidene derivatives of methyl acetoacetate and acetylacetone, diethyl 2,4-bis(trifluoroacetyl)-3-phenylpentanedioate, or dimethyl 2-aryl-4-hydroxy-6-oxocyclohexane-1,3-dicarboxylates. The reactions of the resulting 2-arylidene derivatives with O-methylisourea in the [Bmim][BF4] ionic liquid produced methyl 2-methoxy-4-methyl-6-aryldihydropyrimidine-5-carboxylates and 1-(2-methoxy-4-methyl-6-phenyldihydropyrimidin-5-yl)ethanone (mixtures of 3,6- and 1,6-dihydro isomers), which were transformed into the corresponding 3,4-dihydropyrimidin-2(1H)-one derivatives.

Cross-condensation of derivatives of cyanoacetic acid and carbonyl compounds. 2. One-pot synthesis of substituted 2-amino-7-methyl-5-oxo-4,5-dihydropyrano[4,3-b]pyrans in ethanol and ionic liquid [bmim][PF6]

The three-component reaction of 4-hydroxy-6-methylpyran-2(2H)-one with cyanoacetic acid derivatives and carbonyl compounds in EtOH or in the ionic liquid, viz., 1-butyl-3-methylimidazolinium hexafluorophosphate ([bmim][PF6]), affords substituted 2-amino-7-methyl-5-oxo-4,5-dihydropyrano[4,3-b]pyrans. The yield of substituted pyrano[4,3-b]pyrans in [bmim][PF6] is by 10—14% higher than that in EtOH.

Regio-, stereo-, and enantioselective reactions of carbon acids catalyzed by recoverable organic catalysts bearing ionic liquid moieties

Organic compounds bearing specific ionic liquid (IL) moieties, in particular, bulky organic cations and fluorinated organic or inorganic anions, catalyze many important reactions of carbon acids involving carbanions and enols as reactive species, such as aldol, Michael, and dichlorocyclopropanation reactions. Many of these catalysts are at least comparable to traditional phase-transfer catalysts (PTCs) with halide anions or organocatalysts based on amino acid derivatives. Furthermore, they enjoy the advantage of being readily recoverable and hence are available for multiple recycling in chemical reactions.

Cross-coupling of polychlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salts as catalytic systems

The reactions of di-, tetra-, and hexachlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salt-base as catalytic systems afford cross-coupling products in moderate yields. The highest conversions are attained when imidazolium salts bearing bulky aromatic substituents are used and the reaction is carried out in the presence of alkali alkoxides containing Hα atoms. Cross-coupling is accompanied by hydrodechlorination of aromatic C-Cl bonds.

Reactions of β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane with 3-(dicyanomethylidene)indan-1-one and 1,3-bis(dicyanomethylidene)indane

Reactions of 3-(dicyanomethylidene)indan-1-one and 1,3-bis(dicyanomethylidene)indane with β-dimethylaminoacrolein aminal, 3-dimethylamino-1,1,3-trimethoxypropane, DMF acetal, and ethyl orthoformate were studied. The reaction of 3-(dicyanomethylidene)indan-1-one with 3-dimethylamino-1,1,3-trimethoxypropane gave the 1,3-bis(1-dicyanomethylidene-3-oxoindane)trimethineoxanine salt in high yield, which was used to obtain a number of novel cation-anionic polymethine dyes.

One-pot synthesis of substituted styrenes from vicinal dibromoalkanes and arylboronic acids

Dehydrobromination of vicinal dibromoalkanes in systems comprising 1,2-dimethoxy-ethane, N-butyl-N′-methylimidazolium tetrafluoroborate (or tetrabutylammonium bromide), and a base with subsequent palladium-catalyzed cross-coupling of the thus formed bromoalkenes with arylboronic acids furnished substituted styrenes.

Reactions of CH-acids with α,β-unsaturated aldehydes in ionic liquids

Metal carbonate-catalyzed reactions of CH-acids (diethyl malonate, ethyl acetoacetate, ethyl cyanoacetate, and ethyl 2-acetyl- and 2-ethoxycarbonyl-5,9-dimethyldeca-4,8-dienoates) with α,β-unsaturated aldehydes (acrolein, crotonaldehyde, citral) were studied in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], and in a 1-butyl-3-methylimidazolium bromide ([bmim][Br]) — benzene system. The reactions with acrolein and crotonaldehyde afforded Michael addition products, those with citral resulted in Knoevenagel addition products. Sonication increased the yields of the Michael adducts. The ionic liquid [bmim][PF6] can be recovered and repeatedly used in the reactions.