Chromium (low valent)
The stereoselective reaction of different aldehydes and ethyl dibromoacetate promoted by SmI2 or CrCl2 gives (E)-α,β-unsaturated esters by an an aldol-type reaction and a subsequent β-elimination reaction.
J. M. Concellon, C. Concellon, C. Mejica, J. Org. Chem., 2005, 70, 6111-6113.
Slow addition of a terminal alkyne and water to a mixture of an aldehyde, CrCl2, NiCl2 and a catalytic amount of triphenylphosphine in DMF at 25°C generates a 1,2-disubstituted allylic alcohol regioselectively.
K. Takai, S. Sakamoto, T. Isshiki, Org. Lett., 2003, 5, 653-655.
Electrochemical Nozaki-Hiyama-Kishi Coupling: Scope, Applications, and Mechanism
Y. Gao, D. E. Hill, W. Hao, B. J. McNicholas, J. C. Vantourout, R. G. Hadt, S. E. Reisman, D. G. Blackmond, P. S. Baran, J. Am. Chem. Soc., 2021, 143, 9478-9488.