By example of conjugate addition of 2-nitropropane to 2-cyclohexen-1-one, it is shown that the combination of H-Leu-His-OH and (1R,2R)-(+)-1,2-diphenylethylenediamine as co-catalysts in a suitable ratio can lead to a new catalytic system for the C-C bond formation reactions. Although neither co-catalyst is sufficiently effective independently in terms of yield or enantioselectivity, their combination results in a drastic increase in yields (up to 86%) and absolute selectivities (up to 91% ee).The recent contributions by several groups in the field of asymmetric synthesis with amino acids 1 and short-chain peptides 2 as efficient chiral catalysts appear to be very interesting for chemists from academia as well as from industry. 3 Although amino acids such as proline and phenylalanine and derivatives have been used for a long time in enantioselective catalytic reactions, 4,5 the use of peptide-like enzyme mimics is a recent development and continues to receive growing interest for the C-C bond forming reactions.The Michael addition is one of the most frequently used C-C bond formation reactions in organic synthesis. 6 The development of asymmetric methodologies for this type of reaction has not only broadened its scope and applicability but has also provided insight into fundamental stereochemical aspects important to other carbon-carbon bond forming reactions such as Strecker synthesis, aldol and Diels-Alder reactions.Proline 1c,e and N-terminal prolyl di-and tripeptides 2e,g have been reported recently as organic catalysts for asymmetric Michael additions.To the best of our knowledge, no report is known of proline-free dipeptides catalyzing such reactions.Herein we report a new catalytic system, based on dipeptides, for C-C bond formation reactions by example of asymmetric Michael additions.The formation of C-C bonds by conjugate addition of appropriate carbanionic reagents to a,b-unsaturated carbonyl compounds is one of the most useful methods of remote functionalization in organic synthesis. 1c,6 Initially, we evaluated various dipeptides (H-Phe-His-OH, H-His-Phe-OH, H-Lys-Phe-OH, H-Leu-Arg-OH, H-Val-Arg-OH, HLys-Arg-OH, H-Lys-Tyr-OH, H-Lys-His-OH, H-HisLeu-OH, H-Leu-His-OH) as catalysts for the known asymmetric conjugate addition of 2-nitropropane to 2-cyclohexen-1-one (Scheme 1). Scheme 1Reactions were run at room temperature in DMSO or DMF under conditions employing 15 mol% of dipeptide and trans-2,5-dimethylpiperazine (3) as additive (Figure 1). 7 The peptides H-Leu-His-OH (1) and H-HisLeu-OH (2) were found to be the most promising dipeptide catalysts regarding enantioselectivities and yields. In DMSO much better yields (53%, 95%; entries 1 and 3, respectively), but overall lower enantioselectivities (29%, 26% ee, respectively) were observed in the presence of peptides 1 and 2, relative to the results in less polar DMF (24%, 29% yields and 31%, 41% ee, entries 2 and 4 of Table 1, respectively). Peptide 1 in the absence of additives gave the R-product in DMSO with 13% yield and 42% ee (entry 5) and in DMF w...

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-

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A new organocatalytic system, novel chiral bisformamide and in situ generated L-proline-derived allylsilane reagent , which converts different aldimines to homoallylic amines in good to high yields (up to 95%) and good enantioselectivities (up to 85% ee) has been described.

Enantioselective syntheses O 0031 4-trans-Amino-Proline Based Di-and Tetrapeptides as Organic Catalysts forAsymmetric C-C Bond Formation Reactions. -Peptide catalysts DIP and TEP are successfully applied in the conjugate addition of nitroalkanes to cyclic enones, and in the direct aldol reaction of nitrobenzaldehyde with acetone. In the latter case, the peptide catalysts are significantly more active than L-proline and the catalyst loading can be reduced from 30 to 5 mol%. -(TSOGOEVA*, S. B.; JAGTAP, S. B.; ARDEMASOVA, Z. A.; Tetrahedron: Asymmetry 17 (2006) 6, 989-992; Inst. Org.