Trends in Asymmetric Michael Reactions Catalysed by Tripeptides in Combination with an Achiral Additive in Different Solvents

Abstract

The potential of tripeptides 3, 6 and 12 as chiral catalysts for asymmetric Michael addition reactions in the presence of an achiral additive has been tested in different solvents (CHCl 3 , acetone, DMF, DMSO and the room-temperature ionic liquid [bmim]PF 6 ). The dependence of yields and enantiomeric excesses on the solvent used has been demon-

Recent Advances in Asymmetric Organocatalytic 1,4‐Conjugate Additions

“…Subsequently we demonstrated [8,9] that an asymmetric version of the addition of different nitro alkanes to cyclic enones can be successfully achieved with short peptides based on 4-trans-aminoproline as catalysts (Scheme 1). In the presence of the di-, tri-, and/or tetrapeptide as the catalyst (2 mol-%) and trans-2,5-dimethylpiperazine as an additive, the products have been formed in up to 100 % yield and with up to 88 % ee.…”

Are Ionic Liquids Suitable Media for Organocatalytic Reactions?

“…The reaction was performed in various solvents ([bmim]PF 6 , DMSO, DMF, or iPrOH), but no significant differences were observed between them. The catalytic system in the ionic liquid was recycled three times with constant yields and selectivity, but the reaction times had to be prolonged from 24 to 100 h. Tsogoeva et al [45] investigated the Michael addition of 2-nitropropane to cyclohex-2-enone catalyzed by several tripeptide organocatalysts, such as 16 (Figure 2). Interestingly, the addition in [bmim]PF 6 was slower than that in organic solvents such as CHCl 3 , DMF, or DMSO.…”

Organocatalytic Reactions Under Unusual Conditions

“…The reaction was performed in various solvents ([bmim]PF 6 , DMSO, DMF or iPrOH), but no significant differences were observed between them. The catalytic system in ionic liquid was recycled 3 times with constant results in terms of yields and selectivity, but reaction time had to be prolonged from 24 to 100 h. Tsogoeva et al [112] catalyzed Michael addition of 2-nitropropane to cyclohex-2-enone with several tripeptide organocatalysts, such as C71. Interestingly, the addition was slower in [bmim]PF 6 , compared with reaction in organic solvents, such as CHCl 3 eral proline-derived diamine catalysts.…”