Michael additions of α-nitroesters with enones and α,β-unsaturated aldehydes result in quantitative conversions to the corresponding 1,4-adducts by performing the reactions in water in the presence of ytterbium triflate as water-tolerant Lewis acid.
Keller, E., & Feringa, B. L. (1997). Highly Efficient Ytterbium Triflate Catalyzed Michael Additions of α-Nitroesters in Water. Synlett, 1997(7), 842–844. https://doi.org/10.1055/s-1997-5761