Hydroxyketones, asymmetric hydrogenation

Asymmetric reduction The ruthenium(II)-BINAP catalysts developed by Noyori s group in 1980s were the most successful for the asymmetric hydrogenation of functionalized ketones such as a-ketoesters, a-hydroxyketones and a-aminoketones because the second... 

The alkylation of asymmetric acyclic ketones takes place regioselectively on the most-substituted carbon, thus affording the syn isomers as major products. a-Hydroxyketones showed anti selective additions similar to that observed in related aldol, and Mannich-type additions (Scheme 2.39). Such selectivity is due to the preferred formation of the Z-enamine intermediate, stabilized by intramolecular hydrogen bonding between the hydroxy group and the tertiary amine of the catalyst [23]. 

Acyclic chiral a-amino acids or derivatives are also effleient eatalysts for the asymmetric two- or three-components Mannich reaction. Protected or free 2-hydroxyketones reacted with 16 in the presence of L-tiyptophan, O-protected-L-threonine or L-serine and generally led to the a ft-adduct 17, explained by the formation of a (Z)-enamine stabilised by an intramolecular hydrogen bond (Scheme 12.5). Threonine surfactant 14 was equally effective for the three-component reaction with hydro gracetone, benzalde-hyde derivatives and anilines. ... 

List and coworkers reported an oxa-Michael reaction with aliphatic acyclic enones 94 using hydrogen peroxide as oxygen source [111]. Treatment of enones with catalytic amounts of cinchona alkaloid derived primary amine 33 (as its salt), followed by excess hydrogen peroxide furnished the intermediate peroxy-hemiketals with high yields and stereoselectivities. Subsequent reduction of these compounds led to the corresponding p-hydroxyketones 124 without loss of enantioselectivity (Scheme 33.36). The same research group developed the asymmetric epoxidation of enones with excellent results [112],... 

Scheme 8.43)." The aldol reaction of aldehyde 272 and alkynylketone 273 catalyzed with Zn(ll)-265 complex gave (3-hydroxyketone 274 in excellent stereoselectivity. Noyori hydrogen transfer reaction provided the central diol moiety of fostriecin 278. They accomplished the asymmetric synthesis of 277, therefore, the formal synthesis of fostriecin 278. 

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