Asymmetric Mannich, a-Aminoxylation, and Diels-Alder Reaction

Entry Catalyst (mol%) Additive or solvent T(h) Yield (%) syn/anti ee (%) 

Recently, some extensive research has been devoted to exploring a diastereo-selective and enantioselective route for the synthesis of a-hydroxyaldehydes or a-hydroxyketones because they are important building blocks for the construction of complex natural products and biologically active molecules [91]. In parallel with the transition-metal-catalyzed asymmetric nitroso-aldol reaction [92], much interest has also been expressed towards the proline-catalyzed direct asymmetric a-aminoxylation of aldehydes or ketones for the synthesis of optically active a-hydroxyladehydes and a-hydroxyketones [93]. Wang [94] and Huang [95] independently reported an L-proline-catalyzed asymmetric a-aminoxylation reaction in ionic liquids, whereby it was found tliat aldehydes and ketones could undergo 

Asymmetric Diels-Alder reactions in ionic hquids have been conducted using the privileged MacMillian s catalyst imidazohdin-4-one 51 [97]. The Diels-Alder reachons between cyclohexadiene and acrolein were carried out using 5 mol% of 

Enantioselective Catalysis in Supercritical Carbon Dioxide (scCOj) 

5 Enantioselectii/e Catalysis in Supercritical Carbon Dioxide (scCO2) 277 [Rh52(COD)]X 0.1 mol%) = 

---