Nitroaldol reaction, anti-selective catalytic

Nd/Na heterobimetallic complex promoted an anti-selective catalytic asymmetric nitroaldol reaction. The... 

Heterobimetallic Catalysis with Amide-Based Ligand 3.1 Anti-Selective Catalytic Asymmetric Nitroaldol Reaction... 

Scheme 8 Anti-selective catalytic asymmetric nitroaldol reaction promoted by the heterogeneous Nd/Na heterobimetallic catalyst...

Based on catalytic double activation (guanidinium salt/thiourea moiety skeleton), Nagasawa et al. were able to achieve the reaction of nitromethane, nitro-ethane, and nitropropane with aliphatic a-ketoesters in moderate yields and selectivities (Scheme 29.10) [24]. The reaction works with the assistance of 10 mol% KOH and to overcome the retro-nitroaldol reaction, the presence of 50mol% K1 was required. The resulting Henry reaction adducts are obtained with good syn/anti ratios, and enantioselectivities of up to 98%. When aromatic a-ketoesters were subjected to the reaction unsatisfactory results were obtained (e.g., R = Ph, 5% yield and 5% ee). 

The nitroaldol (Henry) reaction provides 1,2-nitro alkanols under atom-economical proton transfer conditions, which allows for easy access to highly versatile 1,2-amino alcohols (Scheme 6) [31]. A number of catalytic systems have been devised to render this useful C-C bond-forming reaction asymmetric however, diastereoselectivity remained a longstanding problem, in particular for a ri-selective reactions [14, 32, 33]. syw-Selective reaction can be achieved by a monometalhc catalytic system as shown in Fig. 9a, where both an aldehyde and a nitronate coordinate to the metal center to give syn product due to steric repulsion [34—36]. To make the reaction proceed in fluft-selective manner, different strategy in catalyst design is required [37, 38]. Simultaneous activation of both the aldehyde and the nitronate in an anti-paraUel fashion can afford the anti-1,2-nitro alkanols preferentially (Fig. 9b). To attain the a ri-paraUel transition state, a heterobimetalhc catalyst offers a suitable... 

---