[1][2][3] The active reductant is described as "cerium borohydride", which is generated in situ from NaBH4 and CeCl3(H2O)7.
[5] An enone forms an allylic alcohol in a 1,2-addition, and the competing conjugate 1,4-addition is suppressed.
The selectivity can be explained in terms of the HSAB theory: carbonyl groups require hard nucleophiles for 1,2-addition.
In one application, a ketone is selectively reduced in the presence of an aldehyde.
Actually, in the presence of methanol as solvent, the aldehyde forms a methoxy acetal that is inactive in the reducing conditions.