Henry reaction nitronates condensation

Silyl Nitronates in Henry Reactions Topologically, condensations of SENAs with carbonyl and nitroso groups, as well as with an imino fragment, belongs to Henry reactions. 

The Sowden homologation [21], based on the nitroaldol condensation (Henry reaction) [22] between the aldehydo sugar and nitromethane in basic medium, followed by the Nef decomposition [23] of the resultant nitronate in strongly acidic conditions, has been employed in a more limited number of cases than the cyanohydrin synthesis. A recent example in this area is shown by the stepwise homologation of (V-acetyl-D-mannosamine (11) into /V-acetylneuraminic acid (12) [24] (Scheme 4). Also, this procedure has found... 

It is reported that catalytic amount of Lewis acid promotes nitroaldo condensation of imine 49 with nitronates 50 to form 2-nitroamines 51, which can be reduced to diamines 52 with 15 1 syn/anti ratio after removal of the protection group. This seminal work just sets up the stage for the development of catalytic asymmetric aza-Henry reaction. For instance, copper based chiral Lewis acid with C2-symmetry 53 is used to promote addition of nitropropane to imine 54 to form intermediate 2-nitroamine 55 with high diastereo- and enantio-selectivities, which can be further elaborated to afford chiral diamine 56. ... 

The condensation of nitro compounds and imines, the so-called aza-Henry or nitro-Mannich reaction, has recently emerged as a powerful tool for the enantioselective synthesis of 1,2-diamines through the intermediate /3-amino nitro compounds. The method is based on the addition of a nitronate ion (a-nitro carbanion), generated from nitroalkanes, to an imine. The addition of a nitronate ion to an imine is thermodynamically disfavored, so that the presence of a protic species or a Lewis acid is required, to activate the imine and/or to quench the adduct. The acidic medium is compatible with the existence of the nitronate anion, as acetic acid and nitromethane have comparable acidities. Moreover, the products are often unstable, either for the reversibility of the addition or for the possible /3-elimination of the nitro group, and the crude products are generally reduced, avoiding purification to give the desired 1,2-diamines. Hence, the nitronate ion is an equivalent of an a-amino carbanion. 

The nitroaldol condensation with nitromethane (Henry s reaction), followed by Nef decomposition of the resultant nitronate under strongly acidic conditions, has been used to elongate aldehydes. For instance, A-acetyl-D-mannosamine has been converted into A-acetylneuraminic acid applying this method iteratively [69]. Chikashita and coworkers [70] have reported good levels of anti diastereoselectivity better than 99% in an iterative homologation sequence using 2-lithio-l,3-dithiane [71] with 2,3-O-cyclohexylidene-D-glyceraldehyde R)-62. In the case of the BOM-protected tetrose derivative, the addition of 2-lithio-l,3-dithiane was syn selective (synlanti 82 18) (Scheme 13.30). 

The nitroaldol condensation with nitromethane (Henry s reaction), followed by Nef decomposition of the resultant nitronate under strongly acidic conditions has been used to elongate aldehydes. For instance, A-acetyl-D-mannosamine has been converted into A-acetylneu-... 

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