A new organocatalyst derived from abietic acid and 4-hydroxy-l-proline for direct asymmetric aldol reactions in aqueous media

Enantioselective direct aldol reactions were carried out in aqueous media with a new organocatalyst that was derived from 4-hydroxy-l-proline and abietic acid via a simple and convenient synthetic protocol with a high overall yield (75%). The new organocatalyst was used for aldol reactions between substituted aromatic aldehydes and various ketones in the presence of several acid additives in aqueous media. The corresponding aldol products were obtained in high isolated yields (up to 99%) and with high anti-diastereoselectivities (up to 94%) and enantioselectivities (>99.9%). The catalyst loading can be efficiently reduced to only 1 mol %. The aldol reactions were found to be extremely fast which is very unusual in organocatalyzed reactions in water.     

Highly efficient and solvent-free direct aldol reaction catalyzed by glucosamine-derived prolinamide

The catalytic activity of novel sugar-based prolinamides in the aldol reaction between ketones and aryl aldehydes has been examined. The prolinamide 1c was found to be an efficient organocatalyst for the asymmetric aldol reaction under solvent-free conditions. A variety of ketones and aldehydes were used as substrates and the corresponding aldol products were obtained in excellent chemical yields with high levels of anti diastereoselectivity (up to 99:1) and enantioselectivity (up to >99%).     

Efficient ball-mill procedure in the ‘green’ asymmetric aldol reaction organocatalyzed by (S)-proline-containing dipeptides in the presence of water

The organocatalytic activity of (S)-proline-based dipeptides 1a-c has been evaluated in the asymmetric aldol reaction between representative ketones with various aromatic aldehydes under solvent-free conditions in a ball mill. In particular, the methyl ester of (S)-proline-(S)-tryptophan, (S,S)-1c, proved to be an efficient organocatalyst, and the aldol reaction proceeded with good chemical yields and excellent diastereo- and enantioselectivity (up to 98:2 anti/syn dr and up to 98% ee), in the presence of water, and 5 mol % of benzoic acid as additive.     

Direct asymmetric aldol reactions in brine with recyclable fluorous β-aminosulfonamide organocatalysts

Fluorous organocatalyst 3 promotes direct asymmetric aldol reactions of ketones with aldehydes in brine, leading to the synthesis of the corresponding anti-aldol products in high yields with up to 96% ee. Fluorous organocatalyst 3 is easily recovered by solid-phase extraction using fluorous silica gel and can be reused up to five times without purification.     

Thiazolidine-based organocatalysts for a highly enantioselective direct aldol reaction

A set of enantiopure thiazolidine-based organocatalysts have been synthesized from l-cysteine, in a straightforward manner allowing numerous structural variations. In particular, organocatalyst 3a exhibits the highest catalytic performance working in an aqueous medium. It catalyzed the direct catalytic asymmetric intermolecular aldol reaction between unmodified ketones and an aldehyde with excellent stereocontrol and furnished the corresponding aldol products in up to 99% ee. Compound 3a also showed excellent asymmetric catalytic activity in the asymmetric Michael reaction (up to 99% ee).     

Solvent-free asymmetric aldol reaction organocatalyzed by (S)-proline-containing thiodipeptides under ball-milling conditions

An efficient, solvent-free ball-milling protocol for the asymmetric aldol reaction between cyclohexanone and cyclopentanone with various aromatic aldehydes using a novel series of (S)-proline-containing dipeptides and thiodipeptides 1a–f as organocatalysts is reported. In general, (S)-proline-containing thiodipeptides proved to be better organocatalysts relative to their analogous amides. In particular, thiodipeptide (S,S)-1d catalyzed the stereoselective formation of the expected aldol products with excellent diastereo- and enantioselectivity (up to 98:2 anti/syn dr and up to 96% ee). This observation may be ascribed to the increased N–H acidity of the thioamide segment that leads to stronger H-bonding interaction with the aldehyde carbonyl at the transition state and thus higher stereoinduction. Furthermore, thiodipeptide 1f proved to be an efficient organocatalyst for the aldol reaction of acetone with isatin and isatin derivatives (ee 56–86%).     

Camphor-10-sulfonamide-based prolinamide organocatalyst for the direct intermolecular aldol reaction between ketones and aromatic aldehydes

Prolinamides derived from l-proline and N,N-dialkyl 2-aminocamphor-10-sufonamides have been synthesized and used as organocatalysts in the direct intermolecular aldol reaction. Reactions of several aromatic aldehydes with cyclohexanone, cyclopentanone, 4-oxa and 4-sulfa-cyclohexanones and acetone are investigated employing 1a as an organocatalyst. Very high to excellent selectivities are obtained in these direct aldol reactions.     

Additive-controlled regioselective direct asymmetric aldol reaction of hydroxyacetone and aldehyde

A structurally simple dipeptide derivative 1b prepared from l-proline and l-valine has been developed for the direct asymmetric aldol reaction of hydroxyacetone and various aldehydes with moderate to high yields and high enantioselectivities. More importantly, this regioselective reaction could be easily regulated by changing the additives in the presence of the same organocatalyst 1b, to afford the normal 1,2-diol adducts and the disfavoured 1,4-diol products, respectively, in a highly regioselective fashion. A possible reaction mechanism has also been proposed.     

(2S,5S)-Pyrrolidine-2,5-dicarboxylic acid,an efficient chiral organocatalyst for direct aldol reactions

Enantioselective aldol reaction of ketones with aldehydes catalyzed by (2S,5S)-pyrrolidine-2,5-dicarboxylic acid in the presence of an equal molar amount of Et₃N was described. By using the new chiral organocatalyst, the direct aldol condensation products were obtained in reasonable yields and up to 90% ee.     

Hydroxyphthalimide allied triazole-pyrrolidine catalyst for asymmetric Michael additions in water

A new hydroxyphthalimide-coupled triazole-pyrrolidine derivative has been synthesized and demonstrated as an efficient and stereoselective organocatalyst for the asymmetric Michael addition reaction of ketones to nitro olefins at room temperature. Good yields and high selectivities were achieved when benzoic acid was used in combination with organocatalyst 1, employing water as the reaction medium.     

Proline-based dipeptides with two amide units as organocatalyst for the asymmetric aldol reaction of cyclohexanone with aldehydes

A series of proline-based dipeptide organocatalysts with two amide units (1-16) have been developed and evaluated in the direct catalytic asymmetric aldol reactions of aldehydes with cyclohexanone. These catalysts showed good solubility in organic solvents compared with their corresponding carboxyl terminal dipeptides. The robust amide bond formation allowed structural modifications and fine tuning of catalyst properties by varying the stereo and electronic effects of the terminal amide to affect the ability of hydrogen bonding formation between the catalysts and the substrates. The reactions proceeded smoothly in high yields (up to 99%), enantioselectivities (up to 98% ee) and anti-diastereoselectivities (up to 99:1) in the presence of bifunctional organocatalyst 4 under the optimal reaction conditions.     

Synthesis of a biphenyl-based axially chiral amino acid as a highly efficient catalyst for the direct asymmetric aldol reaction

A biphenyl-based axially chiral amino acid (S)-2 has been designed and synthesized. The new amino acid (S)-2 has been found to be a more efficient catalyst than (S)-1 in the direct asymmetric aldol reaction of acetone with aldehydes. For instance, the use of only 0.1 mol % of (S)-2 was sufficient to complete the reaction between acetone and 4-nitrobenzaldehyde, giving the corresponding aldol adduct in good yield with an excellent enantioselectivity.     

Organocatalytic asymmetric syn-selective direct aldol reactions in water

A practical and convenient organocatalytic strategy is developed to provide a direct route to syn-selective aldol products in the presence of water. The siloxy serine organocatalyst mediates the direct aldol reaction of TBSO-protected hydroxyacetone with a variety of aldehydes to provide the aldol products in good yields and enantioselectivities up to 92%.     

Organo-catalyzed highly diastereo- and enantio-selective direct aldol reactions in water

The asymmetric direct aldol reactions of a wide scope of aromatic aldehydes, with unmodified ketones in the presence of 1 mol % of organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and trans-4-hydroxy-l-proline, were performed in water, affording aldol products in high yields with excellent diastereoselectivities of up to >99:1 and enantioselectivities of up to 98%.     

The cooperative effect of a hydroxyl and carboxyl group on the catalytic ability of novel β-homoproline derivatives on direct asymmetric aldol reactions

Novel β-homoproline derivatives, 2-hydroxy-2-(pyrrolidin-2-yl)acetic acids (R,S)- and (S,S)-1a-d, were synthesized. All of the prepared compounds were used as organocatalysts in the direct asymmetric aldol reaction of 4-nitrobenzaldehyde with several ketones. Among these catalysts, (R)-2-hydroxy-2-((S)-pyrrolidin-2-yl)acetic acid (R,S)-1a showed good catalytic ability in the formation of aldol product 13 (up to 69% ee, 95% yield), which was similar to the results catalyzed by l-proline (71% ee, 96% yield). Relatively low yields and low enantioselectivities were observed in aldol reactions catalyzed by (S,S)-1a, for example, 13 was obtained in 55% yield and 13% ee. The aldol reaction catalyzed by the methyl-protected carboxylic acid 1b and esters 1c,d produced much lower chemical yields and enantioselectivities during the formation of 13. The cooperative effect of the (R)-configured hydroxyl group and the carboxyl group was found to play an important role in inducing enantioselectivity in the aldol reaction. Relatively high diastereoselectivities (anti:syn = 85:15) and enantioselectivity (anti, 83% ee) were observed in the aldol reactions of 4-nitrobenzaldehyde with cyclohexanone, which was catalyzed by (R,S)-1a.     

A new chiral primary–tertiary diamine-Brønsted acid salt organocatalyst for the highly enantioselective direct anti-aldol and syn-Mannich reactions

A new primary–tertiary diamine catalyst is easily prepared in a few steps from inexpensive, commercially available, enantiopure materials. This organocatalyst can be effective catalyzed the direct asymmetric aldol and Mannich reactions. The anti-aldol products can be obtained with up to a 99:1 anti/syn ratio and >98 % ee, while the syn-Mannich products could be obtained with up to a 99:1 syn/anti ratio and >99 % ee. Catalyst 1c can be used efficiently on a large scale with the enantioselectivities of the anti-aldol and syn-Mannich reactions being maintained at the same level, which offers a great possibility for application in industry.     

Novel bifunctional sulfonamides catalyze an enantioselective conjugate addition

A new bifunctional organocatalyst with a novel structural and functional motif has been developed. This bifunctional sulfonamide organocatalyst was used in the conjugate addition of 1,3-dicarbonyl compounds (13) to β-nitrostyrenes (12). Yields up to 91% and enantiomeric excesses up to 79% were obtained in this reaction. This catalyst activates both 13 via its basic moiety and 12 through hydrogen bonding.     

Highly stereoselective direct aldol reactions catalyzed by (S)-NOBIN-l-prolinamide

(S)-NOBIN-l-prolinamide was employed as organocatalyst in the direct aldol reactions of different ketones and aromatic aldehydes using dioxane as solvent and in the presence of water as additive. Acetone led to the aldol products in up to 93% ee, while cyclic ketones furnished the anti-aldols in moderate to high yield, excellent diastereoselectivity (up to >99/<1 anti/syn ratio) and high ee (up to 95%).     

以2-氨基-2'-羟基-1,1'-联萘为骨架的有机小分子催化的直接羟醛缩合反应的研究

研究了2-氨基-2'-羟基-1,1'-联萘衍生的有机小分子催化剂催化的直接羟醛缩合反应. 以丙酮为反应物时最好, 得到了99%的收率. 以环酮为底物时, 最高得到99∶1的非对映选择性, 89%的对映选择性.     

Mucohalic acid in Lewis acid catalyzed Mukaiyama aldol reaction: a concise method for highly functionalized γ-substituted γ-butenolides

The first Mukaiyama aldol reaction on mucohalic acid (1a/b) has been achieved. Reaction of 1 with various ketene silyl acetals or silyl enol ethers in the presence of a Lewis acid provides the γ-substituted γ-butenolides in good to excellent yield.