Solvent-dependent enantioswitching in the Michael addition of α,α-disubstituted aldehydes to maleimides organocatalyzed by mono-N-Boc-protected cyclohexa-1,2-diamines

Asymmetric Conjugate Addition of Ketones to Maleimides Organocatalyzed by a Chiral Primary Amine-Salicylamide

Enantioenriched substituted succinimides are interesting compounds, and their asymmetric organocatalytic synthesis by the conjugated addition of ketones to maleimides has been scarcely explored. This study shows the enantioselective conjugate addition of ketones to maleimides organocatalyzed by a simple primary amine-salicylamide derived from a chiral trans-cyclohexane-1,2-diamine, which provides the desired succinimides in good to excellent yields (up to 98%) and with moderate to excellent enantioselectivities (up to 99%).

β-Amino Acid Organocatalysts in the Asymmetric Michael Addition of Isobutyraldehyde to N-Substituted Maleimides

Asymmetric Michael additions of carbonyl compounds to N-substituted maleimides are among the most convenient reactions to prepare optically pure succinimide building blocks. Although a few β-amino acids were found to be highly efficient organocatalysts in the addition of α-branched aldehydes, the effect of their structure on the results of these reactions has not yet been investigated. In the present study, we disclose several unexpected and interesting structural effects of aliphatic and cycloaliphatic β-amino acids obtained in the enantioselective conjugate addition of isobutyraldehyde to N-benzylmaleimide. The dependence of the sense of the enantioselectivity on the bulkiness of the substituent on the β-carbon atom, the beneficial spatial arrangements of the functional groups in cis isomers with cyclohexane scaffold and the inversion of the enantioselectivity depending on the absence of a base additive observed with some trans isomers are unprecedented findings. The minor influence of the nitrogen substituent of the maleimide ring on both the reaction rate and the enantioselectivity was also evidenced using alicyclic β-amino acid prepared from an easily available terpene derivative.

Peptide-Catalyzed Stereoselective Conjugate Addition Reaction of Aldehydes to C-Substituted Maleimides

Catalytic stereoselective additions with maleimides are useful one-step reactions to yield chiral succinimides, molecules that are widespread among therapeutically active compounds but challenging to prepare when the maleimide is C-substituted. We present the tripeptide H-Pro-Pro-Asp-NHC12 H25 as a catalyst for conjugate addition reactions between aldehydes and C-substituted maleimides to form succinimides with three contiguous stereogenic centers in high yields and stereoselectivities. The peptidic catalyst is so chemoselective that no protecting group is needed at the imide nitrogen of the maleimides. Derivatization of the succinimides was straightforward and provided access to chiral pyrrolidines, lactones, and lactams. Kinetic studies, including a Hammett plot, provided detailed insight into the reaction mechanism.

Enantioselective Michael addition of aldehydes to maleimides catalysed by surface-adsorbed natural amino acids

Chiral hybrid materials obtained by adsorption of primary α-amino acids on the surface of inorganic oxides are economic, recyclable, highly enantioselective heterogeneous catalysts for the Michael addition of aldehydes to N-substituted maleimides.

N-Primary-amine tetrapeptide-catalyzed highly asymmetric Michael addition of aliphatic aldehydes to maleimides

The highly asymmetric Michael addition reaction between maleimides and aliphatic aldehydes catalyzed by low-loading β-turn tetrapeptides with excellent yields and enantioselectivities at room temperature was reported. α-Branched and α-unbranched aldehydes both are suitable nucleophiles. N-Aryl, alkyl and hydrogen maleimides all are well tolerated and led to high yields and enantioselectivities. The transformation can be enlarged to the gram scale without decrease in the yield and enantioselectivity. Furthermore, the succinimides were converted into γ-lactams and γ-lactones, showing good practicality of this work. Some reaction intermediates in the proposed reaction mechanism can be captured with the HR-MS method.

Green Asymmetric Organocatalysis

Asymmetric organocatalysis is becoming one of the main tools for the synthesis of chiral compounds that are needed as medicines, crop protection agents, and other bioactive molecules. It can be effectively combined with various green chemistry methodologies. Intensification techniques, such as ball milling, flow, high pressure, or light, bring not only higher yields, faster reactions, and easier product isolation, but also new reactivities. More sustainable reaction media, such as ionic liquids, deep eutectic solvents, green solvent alternatives, and water, also considerably enhance the sustainability profile of many organocatalytic reactions.

A solvent-dependent chirality-switchable thia-Michael addition to α,β-unsaturated carboxylic acids using a chiral multifunctional thiourea catalyst

An asymmetric thia-Michael addition of arylthiols to α,β-unsaturated carboxylic acids using a thiourea catalyst that bears arylboronic acid and tertiary amine moieties is reported.

An asymmetric thia-Michael addition of arylthiols to α,β-unsaturated carboxylic acids using a thiourea catalyst that bears arylboronic acid and tertiary amine moieties is reported. Both enantiomers of the Michael adducts can be obtained in high enantioselectivity and good yield merely by changing the solvent. The origin of the chirality switch in the products was examined in each solvent via spectroscopic analyses.

The effect of chiral N-substituents with methyl or trifluoromethyl groups on the catalytic performance of mono- and bifunctional thioureas

We evaluated thiourea organocatalysts that incorporate a chiral group which includes a trifluoromethyl moiety and contrasted their performance with non-fluorinated analogs. The comparison between such systems allows the direct study of the NH acidity of a thiourea bonded to an aliphatic substituent. In principle, -CF3 systems feature an enhanced hydrogen bond (HB) donor capacity that is undoubtedly beneficial for HB-catalysis applied to the Baylis-Hillman reaction. We found that the thiourea substituted on both nitrogens with this group accelerates this reaction like Schreiner's thiourea. On the other hand, we observed a different behavior in reactions promoted by bifunctional catalysts (thiourea-primary amine). In the Michael addition of isobutyraldehyde to methyl benzylidenepyruvate, the -CF3 containing catalysts were better than the -CH3 systems, whereas the conjugate addition to N-phenylmaleimide showed the opposite behavior. Theoretical calculations of the transition states indicated that the phenylethyl group in fluorinated and non-fluorinated compounds have different kinds of interactions with the electrophile. These interactions are responsible for a different arrangement of the electrophile and thereby the selectivity of the catalyst. Therefore, it cannot be generalized that in all cases NH acidity correlates with the performance of the catalyst, particularly, with aliphatic substituents that unlike the aromatic ones possess groups that are outside the plane of the thiourea.

Enantioselective Michael Addition of Aldehydes to Maleimides Organocatalyzed by a Chiral Primary Amine-Salicylamide

A primary amine-salicylamide derived from chiral trans-cyclohexane-1,2-diamine was used as an organocatalyst for the enantioselective conjugate addition of aldehydes, mainly α,α-disubstituted to N-substituted maleimides. The reaction was performed in toluene as a solvent at room temperature. The corresponding enantioenriched adducts were obtained with high yields and enantioselectivities up to 94%. Theoretical calculations were used to justify the stereoinduction.

Asymmetric Conjugate Addition of α,α-Disubstituted Aldehydes to Nitroalkenes Organocatalyzed by Chiral Monosalicylamides from trans-Cyclohexane-1,2-Diamines

Primary amine-salicylamides derived from chiral trans-cyclohexane-1,2-diamines are used as organocatalysts for the enantioselective conjugate addition of α,α-disubstituted aldehydes to arylated and heteroarylated nitroalkenes. The reaction is performed in the presence of 4-dimethylaminopyridine as an additive in dichloromethane as a solvent at room temperature. The corresponding enantioenriched γ-nitroaldehydes are obtained with enantioselectivities up to 95%. Theoretical calculations are used to justify the reasons of the stereoinduction.

Asymmetric Michael Addition Organocatalyzed by α,β-Dipeptides under Solvent-Free Reaction Conditions

The application of six novel α,β-dipeptides as chiral organocatalysts in the asymmetric Michael addition reaction between enolizable aldehydes and N-arylmaleimides or nitroolefins is described. With N-arylmaleimides as substrates, the best results were achieved with dipeptide 2 as a catalyst in the presence of aq. NaOH. Whereas dipeptides 4 and 6 in conjunction with 4-dimethylaminopyridine (DMAP) and thiourea as a hydrogen bond donor proved to be highly efficient organocatalytic systems in the enantioselective reaction between isobutyraldehyde and various nitroolefins.

Solvent effects in catalysis: implementation for modelling of kinetics

A mathematical framework is developed for analysis of solvent dependent reaction rates and selectivity in the case of complex catalytic reactions by incorporating solvent permittivity into the rate expressions.

Maleimide as an efficient nucleophilic partner in the aza-Morita–Baylis–Hillman reaction: synthesis of chiral 3-substituted-3-aminooxindoles

A highly enantioselective β-isocupreidine catalyzed aza-Morita–Baylis–Hillman reaction of maleimides with isatin derived ketimines provides 3-substituted-3-aminooxindoles with enantiomeric excess upto 99%.