Nitroalkenes transfer hydrogenation

Scheme 6.54 Chiral nitroalkanes provided from the 54-catalyzed asymmetric transfer hydrogenation of nitroalkenes in the presence of 55.

Blechert, Thomas, and co-workers developed a microporous recyclable heterogeneous catalyst 155 based on chiral phosphoric acid, which has been utilized in transfer hydrogenation, aza-ene-type reaction, and AFC alkylation of pyrrole. In the presence of 5 mol% polymer-supported catalyst 155, the AFC alkylation of pyrrole with nitroalkene occurred smoothly to afford the desired product in 91% yield with 96% ee (Scheme 6.71). 

Simultaneously, although independently, Bemardi, Fochi and co-workers developed an extraordinary additional example of highly enantioselective transfer hydrogenation using ]S-trifluoromethyl nitroalkenes to give easy access to optically active jS-trifluoromethyl amines with excellent results [162]. 

Scheme 6.104 Key intermediates of the proposed catalytic cycle for the 100-catalyzed Michael addition of a,a-disubstituted aldehydes to aliphatic and aromatic nitroalkenes Formation of imine (A) and F-enamine (B), double hydrogen-bonding activation of the nitroalkene and nucleophilic enamine attack (C), zwitterionic structure (D), product-forming proton transfer, and hydrolysis.

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