Organocatalytic reactions, enantioselection Henry reaction

On the other hand, Palomo et al. have developed efficient organocatalytic asymmetric aza-Henry reactions under phase-transfer conditions. This method was based on the reaction of a nitroalkane with an azomethine generated from an a-amido sulfone promoted by CSOH.H2O as a base in toluene and in the presence of cinchonine-derived ammonium catalysts. The corresponding. syw-products were obtained in good yields, moderate to good diastereoselectivities (10-86% de) and moderate to excellent enantioselectivities... 

Jia, Z.-X., Luo, Y.-C., Xu, P.-F. (2011). Highly enantioselective synthesis of polysub-stituted tetrahydroquinolines via organocatalytic Michael/Aza-Henry tandem reactions. Organic Letters, 13, 832-835. 

Jhuo, D.-H., Hong, B.-C., Chang, C.-W., Lee, G.-H. (2014). One-pot organocatalytic enantioselective Michael-Michael-Aldol-Henry reaction cascade. A facile entry to the steroid system with six contiguous stereogenic centers. Organic Letters, 16, 2724-2727. 

Recently, asymmetric reactions catalyzed by metal-free compounds (organoca-talysis) have received increased attention due to the potential advantages of these types of systems [4]. This is primarily due to the operational simpUcity and the obvious industrial applications. This chapter covers recent developments, from 2007 to date, in the area of the enantioselective organocatalytic Henry reaction with an emphasis on catalytic methods based on Bronsted bases, Bronsted acids, and phase-transfer conditions (PTC) approaches. 

Organocatalytic Henry reactions with synthetically useful levels of yields and enantioselectivities came a decade later with the independent work of Nagasawa and Hiemstra. Nagasawa used guanidinium salt/thiourea brfimctional catalyst 2 for the reaction of nitromethane or nitroethane with aliphatic aldehydes (no reaction was observed when aromatic aldehydes were used) [7]. The reaction works under PTC with the assistance of KOH, and to overcome the retro-nitroaldol reaction K1 as an additive was required (Scheme 29.2). Two years later, the same group extended this reaction to nitroalkanes other than nitromethane, a process that yields the corresponding xyn-nitroalcohols preferentially. 

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