Organocatalysis chiral phosphoric acids

Chiral oxazaborolidine catalysts were applied in various enantioselective transformations including reduction of highly functionalized ketones/ oximes or imines/ Diels-Alder reactions/ cycloadditions/ Michael additions, and other reactions. These catalysts are surprisingly small molecules compared to the practically efficient chiral phosphoric acids, cinchona alkaloids, or (thio)ureas hence, their effectiveness in asymmetric catalysis demonstrates that huge substituents or extensive hydrogen bond networks are not absolutely essential for successful as5unmetric organocatalysis. 

In recent years, several groups have developed enantioselective tandem reactions based on the combination of gold catalysis and organocatalysis. Among them, Gong et al. reported that an achiral gold complex compatibly worked with a chiral phosphoric acid to promote a domino intramolecular hydroamination-reduction reaction, readily transforming... 

Br0nsted acid catalysis, especially with chiral phosphoric acid type catalysts, has become one of the most successful subfields of organocatalysis [9, 10]. However, numerous reactions are still elusive, and the smallest substrates frequently give the poorest selectivity. A probable cause could be traced to a limited interaction of the small substrate with the catalysts structure when approaching its open active site (Scheme 21). With large substrates, the steric interaction is more pronounced, resulting in higher selectivity. 

Phosphoric acids and their derivatives as catafysts Catalytic asymmetric transformations have become an essential part of contemporaiy organic synthesis. Over the past decades, the field of organocatalysis has emerged and grown dramatically with many new applications. In this wide area, chiral phosphoric acids as Bronsted acids... 

Asymmetric hydride reduction using Hantzsch ester has recently been extensively explored in organocatalysis using iminium-based catalysts or Brpnsted acid catalysts [72a-c], As an advance to their asymmetric conterion-directed catalysis (ACDC), List and coworkers found that the combination of simple primary amino acids such as L-valine with a chiral phosphoric acid led to an effective primary aminocatalyst for asymmetric transfer hydrogenation of a,P-unsaturated ketones (Scheme 5.43) [72d]. The catalysis could be applied to a range of substrates with good yields and excellent enantioselectivity. 

Some other very important events in the historic development of asymmetric organocatalysis appeared between 1980 and the late 1990s, such as the development of the enantioselective alkylation of enolates using cinchona-alkaloid-based quaternary ammonium salts under phase-transfer conditions or the use of chiral Bronsted acids by Inoue or Jacobsen for the asymmetric hydro-cyanation of aldehydes and imines respectively. These initial reports acted as the launching point for a very rich chemistry that was extensively developed in the following years, such as the enantioselective catalysis by H-bonding activation or the asymmetric phase-transfer catalysis. The same would apply to the development of enantioselective versions of the Morita-Baylis-Hillman reaction,to the use of polyamino acids for the epoxidation of enones, also known as the Julia epoxidation or to the chemistry by Denmark in the phosphor-amide-catalyzed aldol reaction. ... 

Br0nsted Acid Organocatalysis. The field of Brpnsted add organo-catalysis [151] is clearly dominated by chiral binol-derived phosphoric acids, which after the seminal reports of Akiyama et al. [152] and of Uraguchi and Terada [153] have become one of the most powerful types of organic catalysts [154]. Figure 2.33... 

---