Catalyzes the synthesis of catechin from 3,4-cis-leucocyanidin. Also synthesizes afzelechin and gallocatechin. (2R,3S)-catechin + H2O + NADP(+) = (2R,3S,4S)-leucocyanidin + H(+) + NADPH Flavonoid metabolism; proanthocyanidin biosynthesis. Monomer. Belongs to the NmrA-type oxidoreductase family. Isoflavone reductase subfamily.