When these substrates are reduced, 1,2-reduction - which produces an allyl alcohol - is in competition with the 1,4-reduction - which forms the saturated ketone or aldehyde.
The hydride source Zn(BH4)2 also shows 1,2 selectivity, as well as greater diastereoselectivity; it does so by coordinating not only to the carbonyl oxygen but also to adjacent atoms:[REF] .