Proline‐derived Long‐aliphatic‐chain Amphiphilic Organocatalysts (PDLACAOs) for Asymmetric Reactions in Aqueous Media

Abstract

Herein, a specialized review of the origin and state of the art of proline-derived long-aliphatic-chain amphiphilic organocatalysts (PDLACAOs) and their use in asymmetric organic reactions in aqueous media (water, brine, and sea water), including in water and in the presence of water, is presented. The reactions in which they have been evaluated and the most important mechanisms are discussed. Scheme 24. Michael addition reaction of dicyanoolefins 57 to α,β-unsaturated aldehydes 48 in-brine using catalyst 46 g, by Loh. Scheme 25. Michael addition reaction in brine using catalysts 59 a-c, by Ni and Headley. Scheme 26. Cross-aldol reaction using catalyst 59 c in the presence of ionic liquid system 64 in brine, by Ni and Headley.

Crossing borders: On‐Water Synthesis of Flavanones

“…For the reaction to occur, a vigorous stirring must be used to favor the formation of small droplets, such stirring must be maintained up to the obtention of the product. Droplets are the necessary hydrophobic environment where the organic reactions are performed, [68,69] since the reaction elapses in heterogeneous medium. Meanwhile, hydrophobic droplets are surrounded by water which provides support, transfer of protons and assists every step of the transformation.…”

On the Influence of a Camphor‐based 1,3‐Diamine Fragment in a Proline‐Based Organocatalyst

“…The concept for the catalysts’ design was to combine a camphor‐based chiral diamine 1 a (Scheme 1), which consists of two chiral amino groups with an α‐amino acid moiety. The two chiral amino groups of the camphor backbone could provide a double‐hydrogen‐bonding interactions (main stabilizing force of the transition state between catalyst and substrate [47] ), and the ( S )‐proline secondary amino group could form an enamine with the carboxyl group of ketones. Since further hydrogen bond donor group would influence the transition state stability, an additional modification of the camphor‐based prolineamide catalyst C1 with a thiourea group, represented by the new catalyst C2 (Figure 2) was pursued.…”

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

“…Asymmetric organocatalysis has become an important area of research in recent years for the preparation of chiral products, being an efficient alternative to enantioselective metal-based catalysis [ 1 , 2 , 3 ]. Since List and Barbas III reported the direct aldol reaction catalyzed by l -proline [ 4 , 5 ], a variety of different organocatalysts have been evaluated for this reaction, but l -proline derivatives still represent some of the best catalysts in this regard [ 6 , 7 ] and have been used successfully in a variety of other reactions [ 8 ]. The aldol reaction continues to be a key carbon–carbon bond-forming reaction, allowing the preparation of enantiomerically enriched β -hydroxy ketones, which are important building blocks for the synthesis of structurally complex molecules with biological activity, and numerous efforts are devoted to improving both yields and stereoselectivities for this reaction [ 9 , 10 , 11 ].…”