obsolete 2-butyl-4-hydroxy-5-methyl-3(2H)-furanoneoxidoreductase activity (obsolete GO:0102980)
OBSOLETE. Catalysis of the reaction: 2-butyl-4-hydroxy-5-methyl-3(2H)-furanone + NADP = (2E)-2-butylidene-4-hydroxy-5-methyl-3(2H)-furanone + NADPH + H+.