Use of (<i>S</i>)‐5‐(2‐Methylpyrrolidin‐2‐yl)‐1<i>H</i>‐tetrazole as a Novel and Enantioselective Organocatalyst for the Aldol Reaction

Tong, Sok-Teng (Amy); Harris, Paul W. R.; Barker, David; Brimble, Margaret A.

doi:10.1002/ejoc.200700834

Cited by 36 publications

(13 citation statements)

References 61 publications

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“…Also, a tandem process consisting of an hydroformylation catalyzed by a rhodium catalyst a d an aldol reaction has been carried out using catalyst 261, with up to 99% ee of the aldol products being achieved [316]. Compound 265 (20 mol%; Figure 3.12) was evaluated in the aldol reaction between acetone (52a, 27 equiv) and aromatic aldehydes in DMSO at 25 • C, with low yields being achieved (11-72%, 70-91% ee), because of the formation of dehydratation products [317]. The application of ''click chemistry'' allowed the synthesis of chiral pyrrolidine-triazole (266, 10 mol%), which was used under solvent-free conditions at 0 • C as catalyst in combination with TFA (1.5 mol%) in the aldol reaction between cyclohexanone (10 equiv) and several aldehydes, leading to the aldol products in good yields and diastereoselectivities, but with low enantioselectivities (86-93% yield, 84-92% de, and 23-28% ee) [318].…”

Section: Ketones As Source Of Nucleophilementioning

confidence: 99%

Organocatalyzed Aldol Reactions

Guillena¹

2013

Modern Methods in Stereoselective Aldol Reactions

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The use of catalytic enantioselective methods to perform an aldol reaction provides a direct entry for the synthesis of chiral compounds and is probably the most attractive way to achieve this goal with high control of the chemo-, regio-, diastereo-, and enantioselectivity. The application of biochemical methods based on enzyme aldolases or antibodies, which are discussed in other chapters, avoid the use of preformed enolates or their equivalents for enhancing the global atom efficiency of the process [1] for which the narrow substrate scope is a major drawback. The discovery of methodologies to carry out the enantioselective direct aldol reaction [2] has eluded the production of stoichiometric by-products increasing the substrate scope. This task could be accomplished by using small molecules as catalysts, such as metal complexes (which are covered along this book) and organic molecules, also known as organocatalysts [3]. The growth of this last research area and the direct aldol reaction are closely linked [4], with the report on the use of (S)-proline as catalyst for the intermolecular aldol [5] definitely being the push for the development of the organocatalytic methods as a competitive methodology for the synthesis of chiral compounds.In a strict sense, an organocatalyzed reaction is a process in which all the involved reagents and catalysis are purely organic compounds of low-molecular weight, excluding boron-and silicon-containing derivatives. However, in some cases, the presence of a silyl group only plays a steric role and therefore can also be considered as an organocatalyzed process. Also, if the organocatalyst involved in a reaction is immobilized in a polymer, a dendrimer, or even an inorganic material that serves only as a support to facilitate its recovery [6], it could still be considered as an organocatalyst, although those types of derivatives have been scarcely used in the natural product synthesis and therefore will be excluded from this chapter. Therefore, a comprehensive overview of the direct aldol reaction [7], emphasizing the reactivity, scope, selectivity, and limitations of the methodology and giving several examples of their application to the synthesis of biologically active compounds, is discussed in this chapter.

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Section: Ketones As Source Of Nucleophilementioning

confidence: 99%

Organocatalyzed Aldol Reactions

Guillena¹

2013

Modern Methods in Stereoselective Aldol Reactions

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“…The syntheses and characterizations of tBoc-l-(aMe)Pro-OH, [49] Z-l-(aMe)Pro-OH, [50] and Z-d-(aMe)Pro-OH [12,13] have already been reported. All newly synthesized compounds were also characterized by 1 H NMR spectroscopy.…”

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Is the Backbone Conformation of C^α‐Methyl Proline Restricted to a Single Region?

Poli

Moretto

Crisma

et al. 2009

Chemistry A European J

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C(alpha)-methyl-L-proline, or L-(alphaMe)Pro, is probably the most conformationally constrained alpha-amino acid. In particular, its omega and phi torsion angles are restricted to about 180 and -60 degrees, respectively, and only three ranges of values are theoretically available for psi in mono- or longer peptides, namely, about -30 degrees (cis', 3(10)/alpha-helical structure), 60 degrees (inverse gamma turn), or 140 degrees (trans', poly(L-Pro)(n) II structure). In this work, we examined the tendency of a number of N(alpha)-acyl dipeptide N'-alkylamides of the type RCO-(alphaMe)Pro-Xxx-NHR' or RCO-Xxx-(alphaMe)Pro-NHR', in which Xxx is L (or D)-Ala, Aib (alpha-aminoisoburyric acid), or L (or D)-(alphaMe)Pro, long enough to fold into intramolecularly hydrogen-bonded gamma or beta turns. The results are compared with those obtained for the corresponding dipeptides based on Pro, a well-known turn-forming residue. For the crystal-state 3D-structural analysis we used X-ray diffraction, whereas our solution conformational analysis was heavily based on the FTIR absorption and (1)H and (13)C NMR spectroscopy techniques. We conclude that (alphaMe)Pro is able to explore both trans' and cis' psi areas of the conformational space, but in (alphaMe)Pro the latter is overwhelmingly more populated, in marked contrast to the Pro preference. This finding is a clear indication that in (alphaMe)Pro the major 3D-structural determinant is the C(alpha)-methyl group. The circular dichroism (CD) signature of a peptide type III' beta-turn conformation is also proposed.

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“…1). [3][4][5][6][7][8][9][10][11][12] It has been convincingly proved by many research ers 13-16 that the presence of an acid component in a cata lytic system and the spatial structure of the catalyst are critical for its activity and stereoselective ability. Based on these data, we obtained new (S) proline derivatives, namely, proline amides containing an alco hol OH group (Scheme 1).…”

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confidence: 99%

New (S)-proline derivatives as catalysts for the enantioselective aldol reaction

et al. 2009

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Use of (S)‐5‐(2‐Methylpyrrolidin‐2‐yl)‐1H‐tetrazole as a Novel and Enantioselective Organocatalyst for the Aldol Reaction

Cited by 36 publications

References 61 publications

Organocatalyzed Aldol Reactions

Organocatalyzed Aldol Reactions

Is the Backbone Conformation of C^α‐Methyl Proline Restricted to a Single Region?

New (S)-proline derivatives as catalysts for the enantioselective aldol reaction

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Use of (S)‐5‐(2‐Methylpyrrolidin‐2‐yl)‐1H‐tetrazole as a Novel and Enantioselective Organocatalyst for the Aldol Reaction

Cited by 36 publications

References 61 publications

Organocatalyzed Aldol Reactions

Organocatalyzed Aldol Reactions

Is the Backbone Conformation of Cα‐Methyl Proline Restricted to a Single Region?

New (S)-proline derivatives as catalysts for the enantioselective aldol reaction

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Is the Backbone Conformation of C^α‐Methyl Proline Restricted to a Single Region?