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

Hernández, José G.; Juaristi, Eusebio

doi:10.1016/j.tet.2011.06.042

Cited by 102 publications

(38 citation statements)

References 81 publications

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“…Dipeptide H-Pro-Trp-OH (169d) in the presence of NMM and SDS in water catalyzed the aldol reaction between cyclic ketones and several aromatic aldehydes yielding the expected products 54 in good yields (67-94%), diastereo-(50-99% de), and enantioselectivities (72-95% ee), with lower enantioselectivity being encountered using acetone as nucleophile (Table 3.12, entry 4) [234]. In this case, the corresponding methyl ester of the dipeptide (169d, 3 mol%) was also used in ball-mill solvent-free reaction conditions in the presence of water (1.1 equiv) and benzoic acid (5 mol%) in the reaction between cyclic ketones and several aromatic aldehydes providing anti-aldols 54 in good results (64-90%, 84-92% de, and 55-98% ee) [235]. Partially protected dipeptide H-Pro-Thr-OH (169e) was evaluated in the aldol reaction between acetone (4 equiv) and several aromatic and aliphatic aldehydes yielding aldol products 54 in good yield (72-91%) and moderate enantioselectivities (65-85% ee) regardless of the nature of the aldehyde [236].…”

Section: Aldehydes As Electrophilesmentioning

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: Aldehydes As Electrophilesmentioning

confidence: 99%

Organocatalyzed Aldol Reactions

Guillena¹

2013

Modern Methods in Stereoselective Aldol Reactions

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“…and up to 98% ee). 97 More recently, O-methyl esters of proline-derived α,β-dipeptides, e.g. (S)-45, have been evaluated, 98 as well as amides supported on MBHA (4-methylbenzhydrylamine) resin, (S)-46.…”

Section: Organocatalysis Via Proline Dipeptide Derivatives Assisted Bmentioning

confidence: 99%

“…Thus, the creation of a hydrophobic pocket enhances non-covalent π-π interactions between aromatic rings present both in the catalyst and in the aldehyde, so that the interaction between these fragments leads to a more rigid transition state, which is translated into a higher stereoselectivity. 97 It is worth mentioning that high-speed ball milling has been recognized as an environment-friendly mechanochemical technique given that it enhances atom economy by diminishing or eliminating solvent usage when carrying out organocatalytic reactions. 107 At this point, it is appropriate to mention that recent advances on separation techniques such as supercritical fluid extraction, 108 solid phase extraction, 109 among other practices 110 might permit a greater level of sustainability in chemical reactions in general.…”

Section: Organocatalysis Via Proline Dipeptide Derivatives Assisted Bmentioning

confidence: 99%

Determination of Enantioselectivities by Means of Chiral Stationary Phase HPLC in Order to Identify Effective Proline-Derived Organocatalysts

Vargas-Caporali¹,

Juaristi²

2017

J. Braz. Chem. Soc.

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The pyrrolidine fragment is a privileged scaffold within chiral ligands employed in coordination complexes exhibiting catalytic activity in asymmetric reactions and, more recently, as enantioselective organocatalysts per se. Likewise, the employment of (S)-proline as starting material constitutes the most direct form to synthesize those chiral derivatives. Afterwards, a preliminary evaluation of the catalytic performance of proline-derived compounds consists of screening many prochiral substrates in well standardized model reactions such as Michael additions and Mannich reactions, with the aim of identifying "broad spectrum" catalysts for more complex synthetic applications. Therefore, a central part of this process involves the fast and direct measurement of enantioselectivities of optically active adducts. The growing development of chiral stationary phases and thus, the wide commercial availability of chiral columns have consolidated high performance liquid chromatography (HPLC) as the preferred technique to identify the most effective catalysts.

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“…Mechanochemistry is mainly promoted by either hand grinding or ball-milling under the solvent-free condition. Indeedly, ball-milling has already been applied for the grinding of minerals into fine particles and the preparation and modification of inorganic solids [26][27][28][29] , but more recently it has rapidly developed in the areas of organic synthesis, e.g., Suzuki [30][31][32] , Sonogashira [33][34][35] , Michael [36][37][38] , aldol reaction [39][40][41][42] , Diels-Alder reaction [43,44] , and so on. Among these, only one recent report by Stolle and co-workers [45] has addressed 1,3-dipolar cycloaddition reaction of azides with alkynes by means of ball-milling, which was named "solvent-free click reaction".…”

Section: Introductionmentioning

confidence: 99%